Barcelona flew to London on Tuesday because of fears of volcanic ash from Iceland drifting towards England ahead of Saturday's Champions League final.
The Spanish side, who face Manchester United in the Wembley final, had been scheduled to travel on Thursday.
However, with ash spreading from the Grimsvotn volcano, Barca brought forward their flight to Tuesday.
Volcanic ash forced Barca to travel by road last year to a Champions League semi-final against Inter Milan.
That came after the Eyjafjallajokull volcano erupted and forced Barca to travel around 600 miles by bus to the San Siro, where they lost the first leg of the tie 3-1.
They won the second leg at the Nou Camp 1-0, but bowed out 3-2 on aggregate.
Europe's air traffic control organisation said on Monday that if volcanic emissions continued at the same rate, the cloud could reach western French and northern Spanish airspace on Thursday.
That could affect the plans of up to 12,000 fans travelling from Catalonia.
Barcelona have vowed to keep their supporters updated, but coach, Pep Guardiola, said: "The final will be on Saturday. Uefa won't change the date of the final.
"Let's hope that the volcano doesn't disrupt travel plans of all the fans who want to go.
"Lots and lots of people - 10,000 or 12,000 people - will travel by plane on the same day and might not be able to change those plans.
"That could be a handicap. It would be terrible to play a final where half of the stands are empty."
Thousands of passengers in Scotland, Northern Ireland and the north of England already face UK flight cancellations because of drifting ash from the Icelandic volcanic eruption.
Airports likely to be affected from 1300 to 1900 BST on Tuesday include Londonderry, Glasgow, Edinburgh, Prestwick, Durham Tees Valley, Newcastle and Carlisle.