Barcelona goalkeeper Marc-Andre ter Stegen believes their one-goal advantage over Manchester United is "not enough to defend" ahead of the return leg of their Champions League quarter-final.
The Spanish champions walked away from Old Trafford with a 1-0 win following Luke Shaw's early own goal but Ter Stegen is wary of a United side that have already upset the odds this season.
Ole Gunnar Solskjaer's side trailed 2-0 at the halfway stage of their last-16 fixture against Paris St Germain, only to stage a remarkable comeback at the Parc des Princes to reach the last-eight.
Ter Stegen said: "The good thing is that we play differently to PSG but they are really dangerous.
"They are very quick. You always have to have be alert. I think it's they key to win this very difficult game. They know how to play in a very calm way. They made things really hard for us (in the first leg).
"The result we got in Manchester is dangerous because it's a very small advantage, it's not enough to defend.
"We need to step forward and create risky situations. We have to keep the ball and create good chances and score."
Ter Stegen's cautiousness could be, in part, due to Barca's shocking downfall against Roma at the same stage of the competition last season.
The Catalan giants seemed to be coasting after claiming a 4-1 victory at the Nou Camp but they were left shell-shocked as their Italian opponents rallied to win 3-0 at the Stadio Olimpico to progress on away goals.
Speaking about the stunning turn of events, Ter Stegen added: "It was hard of course but it's another year on, we got over it.
"We don't want that to happen again. We need to bear it in mind and look forward."
Barca head coach Ernesto Valverde rested several first-team players at the weekend in an effort to keep them fresh for Tuesday night – but the tactic backfired as they were held to a goalless draw by LaLiga's bottom club Huesca.
One positive from the fixture was Ousmane Dembele's return to action after a month on the sidelines because of injury.
The Frenchman played 67 minutes on Saturday and may retain his starting role against United – though Valverde is wary of overburdening the 21-year-old.
"It's a possibility that he may start, he might not" Valverde said. "The other day he played 60 minutes that is what we wanted.
"We didn't want him to play that long but he felt OK, we just wanted to have him ready for this game. I'm not sure he will be able to play for 90 minutes."
