Chelsea boss Antonio Conte says he has had trouble sleeping as his side prepare for Tuesday's Champions League last-16 tie against Barcelona at Stamford Bridge.
The Blues have won just four of their past 12 games in all competitions.
Barcelona are in contention to win the treble and are unbeaten in La Liga, which they lead by seven points, reports the BBC.
"This team is one of the best in the world - maybe they are favourites to win this competition," said Conte.
"On the other hand we must be excited because we have a great opportunity to play a massive game against a really strong team and to show which is our level," the Italian added. "We have to try to have the perfect game."
Chelsea lost their EFL Cup semi-final against Arsenal in January followed by Premier League defeats by Bournemouth and Watford.
They have started to turn their poor form around, with a league win against West Brom on 12 February followed by Friday's FA Cup fifth-round win against Hull.
Conte's future has been the subject of debate this season and following the Barcelona match, his side face a key game against Manchester United in the league on Sunday.
"In these days after the game in the FA Cup, I must be honest... it was a bit difficult to sleep well," said Conte.
"When you have to play this type of game, you have to prepare. You have to prepare everything. You have to prepare big things, but the smaller details too."
Chelsea last beat Barcelona in 2012 in the Champions League semi-finals and went on to win the competition for the first time.
Barca's top scorer this season, Lionel Messi, is yet to score in eight appearances against the Blues.
"We are talking about the best player in the world," added Conte.
"Messi has the capacity to solve situations, create a chance when you are not seeing the chance to score. This means we are talking about a fantastic player."
