London - The volcanic ash plume drifting over Europe is threatening next week's Champions League and Europa League semi-finals.
There are no-fly restrictions over much of Europe, which are unlikely to be relaxed in the coming days.
In the Champions League, Barcelona must travel to Inter Milan for Tuesday's match, while Lyon are playing at Bayern Munich on Wednesday.
Two English sides are away Thursday in the Europa League, with Liverpool at Atletico Madrid and Fulham at Hamburg.
Fulham manager Roy Hodgson said on Saturday that the Premier League club has been in contact with UEFA.
"One of UEFA's concerns is that it should be fair and that their opponents don't have to go through hell and high water to get to the game," Hodgson said. "An ideal scenario would be that the volcanic ash clears up and we can fly over to Germany.
"It's totally and utterly linked to if there are flights. If there are no flights then the only option is to get a train and bus to Hamburg. There could still be a further problem because there might be no trains or coaches to travel on but I'm confident UEFA will resolve the problem."