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.
Solskjaer says that the club cannot look to past successes, including his in 1999, ahead of Tuesday's clash, but tee team can learn from their comeback against Paris Saint-Germain.
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."
Manchester United currently sit fifth in the Premier League as they battle Arsenal, Chelsea and Tottenham for two spots in the top four.
After facing Barca, they'll take on Everton on Sunday in their return to Premier League action.