The Turkish champions face Jose Mourinho's side at home in the first leg of the last-16 tie and the midfielder thinks that they have a good chance of making the next round.
Melo said: "I think we have a 50% chance of winning.
"Chelsea are the leaders in the Premier League but we have analysed some of their games and they are not unbeatable.
"The pressure will be on Chelsea to win and progress so hopefully that will allow us to raise our game to a new level.
"Didier Drogba has talked to us about Chelsea but we have a good squad full of international players."
You can watch Galatasaray v Chelsea on Sky Sports 1 HD from 7.00pm