Lemonis accepted that the Barclays Premier League side are favourites to reach the quarter-finals but his Olympiacos side will not roll over easily.
"Chelsea are not the most spectacular team in Europe, if the truth be told, but they are strong in every aspect and very tough to beat," Lemonis said.
"They are very compact, excellent in defence, and lethal in attack. In games like these, you have to keep errors to a minimum.
"Our chances will depend on how we play defensively, just like in our previous matches in the competition. Chelsea are favourites, of course, but we are determined to put up a fight.
"The only thing that bothers me is when I see my players lacking passion, strength or determination on the pitch.
My only demand for the games against Chelsea is to be proud of our performances afterwards. We are waiting impatiently to see how the coming weeks unfold."