Mbappe has impressed since arriving from PSG over the summer, although many have been expecting more from the Frenchman.
Schuster said at a golf event on Saturday: "Sometimes people like him come in with a lot of quality. Normally it's easier for them, but sometimes it's a bit difficult. I think it's a question of matches. He knows what he has to do, it's a question of time. The whole team has to change a bit, not just him.
"In the team, right now there is no one there (to replace Toni Kroos). He was the last one. He has marked 10 years at Real Madrid with the way of playing. His solidity was only his and that cannot be replaced. There is no one there now and we have to find a formula for things to work the same way.
"There will not be another like him because he has marked an era and this cannot be changed in two months."