However, Mancini was suggesting that perhaps his Cimbom could cause somewhat of an upset at the Turk Telekom Arena in Istanbul.
"Everyone knows Chelsea are one of the best teams in Europe," Mancini said.
"They won [the] Europa League last year and [the] Champions League two years ago. They are used to playing these games every year and we know it will be difficult.
"I think Chelsea are top of the Premier League because they are a top team, with good players who can change the game at any moment. I think they are 80% [likely] to go through in this game.
"It's important we play well in this match because we want to play the return leg in London with some chance."
Galatasaray will travel to west London for the return leg at Stamford Bridge on March 18.
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