The French star is yet to score for Real in La Liga but the coach thinks that a period of adjustment is required following the forward's much-hyped arrival from PSG.
Ancelotti said: "Each year the team changes, the structure of the team changes, that's quite normal.
"Last year we needed time too. Early on, we won a lot of games in the last few minutes. We have to adjust the team a bit this year and find its best version."
Ancelotti also played down concerns about Mbappe's lack of goals as he pointed out that the player netted on his debut in the UEFA Super Cup earlier this month.
The Italian manager said: "We've got a lot of resources. We've had three games and scored six goals, with the team not being at its best. Not scoring goals won't happen, it's never happened here.
"The last goal Mbappe scored was August 14 [in the Super Cup] and today is August 28. That's two weeks. It isn't the time to worry. He isn't worried, and neither are we. VinÃcius [Junior] hasn't scored in three games, and he doesn't look worried."
The work rate off the ball from Real's all-star attack has been questioned by fans and Ancelotti stressed the need for his team to be "compact".
He said: "What we need is a compact team. The work of the forwards is important, and of the defenders. If a forward presses and the defence doesn't step up, the team isn't compact. If the defence drops deep and the forward doesn't drop, the team isn't compact. It isn't about individuals."
