Drogba returns to Stamford Bridge with the Turks tonight for the second leg of the tie, having spent eight successful years with the Blues.
Despite Chelsea being in control of the contest thanks to a 1-1 draw in Turkey two weeks ago, Cahill believes that Drogba will make life difficult for him and his teammates as they look to reach the quarter-finals.
"It is going to be tough with the quality player he is," the England international told the club's official website.
"I have had the pleasure of playing against Didier before I came to Chelsea and I have trained against him a lot, so I know his qualities and he has a lot of them. So it is going to be tough but the game is going to be tough generally."
Chelsea manager Jose Mourinho hinted on Monday that he was keen to bring Drogba back to the club at the end of the season.