Fabregas said that the next two weeks, which include the Milan tie and an El Clasico against Real Madrid in the Copa del Rey, are crucial to the club's season.
"The next two weeks are extremely important," he told the club's official website. "It will be very complicated but we have to have the same confidence that we've had up until now.
"The match against Milan is key because we want to go to Wembley. We believe that they will be a very difficult rival because of the players they have and because of their history. If we aren't at 100% we will not go through to the next round.
"I'm very eager to win the Champions League, and to win it with Barca would be the best present any footballer could hope for."
The first leg of the Copa del Rey semi-final ended 1-1.