Roberto Di Matteo believes Chelsea will need to play two "perfect" games to beat Barcelona in their Champions League semi-final.
Former Blues midfielder Di Matteo has sparked a Chelsea revival since being appointed interim manager six weeks ago after the London club sacked Andre Villas-Boas and last weekend he oversaw a 5-1 FA Cup semi-final victory over capital rivals Tottenham Hotspur at Wembley.
But the 41-year-old predicted Chelsea would have to raise their game still further against reigning European champions Barcelona, already regarded as one of the best club sides of all-time.
The first leg of their semi-final takes place at Stamford Bridge on Wednesday and Di Matteo said: "It's fair to say we need two perfect games.
"But I think, also, that the fact we've been performing very well in the last six weeks gives us the belief we can produce two perfect games in this match.
"It's the biggest challenge for any manager to play against the best team in the world, but for every player as well, to be able to compare themselves against one of the top teams in the world."
Meanwhile, Chelsea mifielder Frank Lampard said it was vital the Blues maintained their discipline, as all three of Chelsea's defeats in 10 matches against Barcelona since 2000 have come when they have had a player sent off.
"Discipline is a huge fact at this level," said Lampard. "To play a man down against Barcelona is very tough.
"We have to tackle and close space, but we've got a good discipline in our team. Keeping 11 on the pitch is crucial."
Chelsea defender David Luiz will miss both Wednesday's match and next week's second leg at Camp Nou with a hamstring injury.