Manchester United goalkeeper David de Gea warned the Red Devils must improve against Barcelona in the Champions League.

United travel to Barcelona on Tuesday trailing 1-0 in the quarter-final tie and struggling for form following their underwhelming Premier League victory against West Ham.

Ole Gunnar Solskjaer's United – who had lost four of their past five games prior to Saturday's fixture – needed a late Paul Pogba penalty to see off West Ham 2-1 at old Trafford.

And De Gea issued a rallying cry ahead of the Camp Nou blockbuster after United failed to register a shot on target at home to Barca in the opening leg.

"Of course it's difficult, but if you want to be a top team you have to play big Champions League games, and the weekend after it's the Premier League," De Gea said.

"So you have to be focused and ready for a difficult game again. I think we didn't play well [against West Ham], we have to improve a lot and now we have a big challenge on Tuesday.

"We will try to fight and win the game. We can go with more confidence after the three points.

"It's a big challenge, a special occasion, in Spain, against Barcelona, a Champions League night, so it's going to be an amazing game.

"We're happy with the win, but at the same time we have to improve a lot."