The Paris club are riding high on top of the Ligue 1 standings, three points clear of second-placed Toulouse and Marseille.
Ibrahimovic, who moved to France from AC Milan in July, has netted 10 of the club's 16 league goals this term, but Ancelotti does not believe his side rely too much on the Swede.
"I don't think we are dependent on Zlatan," Ancelotti said. "We brought him here because he has a strong personality, and a lot of qualities.
"He scores a lot of goals. Every time he scores, it's good for him and for the team. I think the team also works hard for him in order to put him in the best position to score. It's as simple as that."
Wednesday's meeting will be the second clash between PSG and Marseille this season after the two sides shared a 2-2 draw at the Stade Velodrome in the league, and Ancelotti expects another tight contest in the round-of-16 match.
"Marseille are a very good team," he said. "They are physically strong, have a lot of character, and a strong mentality.
"It's a team that will want to beat us because we are becoming fierce rivals.
"It's the same for us - we want to win. In the last game we played against them, with a little bit more consistency, we could have won. (This) game will be the same - closely fought but we can win."