Uefa says it will make a decision "in the coming days" about whether Fulham and Liverpool will travel to Germany and Spain for Europa League ties.
The English clubs have semi-finals on Thursday but the travel chaos sparked by Iceland's volcanic ash cloud has put the matches in doubt.
Fulham boss Roy Hodgson is not keen on making the trip to Hamburg by road.
"It will be a disadvantage if we can't fly and were obliged to find other means of travel," he said.
"One of the major difficulties will be finding that means of travel. We wouldn't be able to contemplate booking anything until probably sometime during Monday, which would make it very late."
For 30 or 40 fans you might find train seats but for the 2,500 who have been really looking forward to this game then it's different
Roy Hodgson
About 2,500 Fulham fans have bought tickets for the game against the German side, and Hodgson feels they will be the losers if they have to make the 450-mile journey should airspace remain closed.
"It would be a disaster for them," said the former Inter Milan boss.
"It would be a real shame. For 30 or 40 people you might find train seats but for the 2,500 who have been really looking forward to this game then it's different."
Liverpool's players and fans have a 900-mile trip to contemplate to reach Spanish capital Madrid for their match against Atletico.
Uefa has already announced the Champions League semi-finals will go ahead on Tuesday and Wednesday.
Barcelona are travelling 450-mile by coach over two days to Italy for Tuesday's first leg against against Inter Milan while French side Lyon will make 360-mile road trip for their tie at Bayern Munich on Wednesday.
606: DEBATE
As ridiculous as this will sound I got a call form my aunt today as she's a flight attendant and has been off work for the last four days but her first flight back will be to accompany Fulham to Germany for the game on Thursday
Matthew
Pep Guardiola, coach of European champions Barcelona, said: "It wouldn't be the best but there are teams from the lower leagues that travel 17 hours by bus.
"A semi-final is enough to help anyone get over any tiredness."
Meanwhile, Newcastle have been forced to make the 400-mile journey to Plymouth for Monday's Championship clash by coach.
Other sports have suffered too. The final leg of the Diving World Series, due to be staged in Sheffield this week, was rearranged to take place in Veracruz, Mexico, following the conclusion of the second leg there on Saturday.
Sunday's MotoGP race in Motegi, Japan, has been re-arranged for 3 October and the Moroccan Golf Classic has also been postponed.
But the Ballantine's Championship in Korea on the full PGA European Tour is unlikely to be affected, with the majority of players already in Asia after the Volvo China Open.
Three-day eventer Oliver Townend was hoping to jet out to Kentucky in a bid to land the Rolex Grand Slam and the £230,000 reward on offer.
Having won at both Badminton and Burghley, the Yorkshireman is chasing the final leg of the Slam - and the lucrative prize - in Lexington.
His trek began in Ellesmere and has taken in Crewe, London and Paris, from where he caught a taxi to Madrid with a view to flying out of the Spanish capital for the USA on Monday afternoon.
Sunday's London Marathon will definitely go ahead as planned but a number of elite athletes, including defending champions Kenyan Sammy Wanjiru and Germany's Irina Mikitenko, could miss out if they are unable to get to Britain.
Elsewhere Olympic cycling champion Bradley Wiggins was forced to miss a road race in the Netherlands.
Great Britain's opening match against Croatia at the Ice Hockey World Championships on Saturday was delayed after the team had to swap a flight for a 26-hour bus and train journey to Slovenia.
Despite not arriving Slovenia until two hours before the game, GB showed no signs of travel fatigue as they coasted to a 4-1 win.
F1 teams battle with volcano mayhem
In rugby league, Widnes Vikings' Challenge Cup tie against Lezignan was postponed and Salford's epic journey by road and ferry to southern France failed to pay off when they were beaten 30-8 by Catalan Dragons.
The start of next weekend's European Gymnastic Championships in Birmingham has been delayed by a day, with the men's competition starting on 22 April, and in cricket Afghanistan have been delayed in their attempt to get to the West Indies for the World Twenty20.
England are due to fly to the Caribbean on Sunday and the England and Wales Cricket Board is "keeping an eye on things".
Officials at Punchestown in Ireland are not expecting the volcanic ash cloud crisis to affect the British raiding party at their big horse-racing meeting this week.
Connections have been quick to make alternative travel plans via ferry.
And in Formula One, although the next Grand Prix is not in Barcelona until 9 May, about 1,000 personnel are stuck in China with teams anxious to get their cars back to factories before too long.
The English clubs have semi-finals on Thursday but the travel chaos sparked by Iceland's volcanic ash cloud has put the matches in doubt.
Fulham boss Roy Hodgson is not keen on making the trip to Hamburg by road.
"It will be a disadvantage if we can't fly and were obliged to find other means of travel," he said.
"One of the major difficulties will be finding that means of travel. We wouldn't be able to contemplate booking anything until probably sometime during Monday, which would make it very late."
For 30 or 40 fans you might find train seats but for the 2,500 who have been really looking forward to this game then it's different
Roy Hodgson
About 2,500 Fulham fans have bought tickets for the game against the German side, and Hodgson feels they will be the losers if they have to make the 450-mile journey should airspace remain closed.
"It would be a disaster for them," said the former Inter Milan boss.
"It would be a real shame. For 30 or 40 people you might find train seats but for the 2,500 who have been really looking forward to this game then it's different."
Liverpool's players and fans have a 900-mile trip to contemplate to reach Spanish capital Madrid for their match against Atletico.
Uefa has already announced the Champions League semi-finals will go ahead on Tuesday and Wednesday.
Barcelona are travelling 450-mile by coach over two days to Italy for Tuesday's first leg against against Inter Milan while French side Lyon will make 360-mile road trip for their tie at Bayern Munich on Wednesday.
606: DEBATE
As ridiculous as this will sound I got a call form my aunt today as she's a flight attendant and has been off work for the last four days but her first flight back will be to accompany Fulham to Germany for the game on Thursday
Matthew
Pep Guardiola, coach of European champions Barcelona, said: "It wouldn't be the best but there are teams from the lower leagues that travel 17 hours by bus.
"A semi-final is enough to help anyone get over any tiredness."
Meanwhile, Newcastle have been forced to make the 400-mile journey to Plymouth for Monday's Championship clash by coach.
Other sports have suffered too. The final leg of the Diving World Series, due to be staged in Sheffield this week, was rearranged to take place in Veracruz, Mexico, following the conclusion of the second leg there on Saturday.
Sunday's MotoGP race in Motegi, Japan, has been re-arranged for 3 October and the Moroccan Golf Classic has also been postponed.
But the Ballantine's Championship in Korea on the full PGA European Tour is unlikely to be affected, with the majority of players already in Asia after the Volvo China Open.
Three-day eventer Oliver Townend was hoping to jet out to Kentucky in a bid to land the Rolex Grand Slam and the £230,000 reward on offer.
Having won at both Badminton and Burghley, the Yorkshireman is chasing the final leg of the Slam - and the lucrative prize - in Lexington.
His trek began in Ellesmere and has taken in Crewe, London and Paris, from where he caught a taxi to Madrid with a view to flying out of the Spanish capital for the USA on Monday afternoon.
Sunday's London Marathon will definitely go ahead as planned but a number of elite athletes, including defending champions Kenyan Sammy Wanjiru and Germany's Irina Mikitenko, could miss out if they are unable to get to Britain.
Elsewhere Olympic cycling champion Bradley Wiggins was forced to miss a road race in the Netherlands.
Great Britain's opening match against Croatia at the Ice Hockey World Championships on Saturday was delayed after the team had to swap a flight for a 26-hour bus and train journey to Slovenia.
Despite not arriving Slovenia until two hours before the game, GB showed no signs of travel fatigue as they coasted to a 4-1 win.
F1 teams battle with volcano mayhem
In rugby league, Widnes Vikings' Challenge Cup tie against Lezignan was postponed and Salford's epic journey by road and ferry to southern France failed to pay off when they were beaten 30-8 by Catalan Dragons.
The start of next weekend's European Gymnastic Championships in Birmingham has been delayed by a day, with the men's competition starting on 22 April, and in cricket Afghanistan have been delayed in their attempt to get to the West Indies for the World Twenty20.
England are due to fly to the Caribbean on Sunday and the England and Wales Cricket Board is "keeping an eye on things".
Officials at Punchestown in Ireland are not expecting the volcanic ash cloud crisis to affect the British raiding party at their big horse-racing meeting this week.
Connections have been quick to make alternative travel plans via ferry.
And in Formula One, although the next Grand Prix is not in Barcelona until 9 May, about 1,000 personnel are stuck in China with teams anxious to get their cars back to factories before too long.
