Mourinho doesn't expect the former Lens defender to be an instant starter.
But he did say: "As for Varane, he is a kid with a great potential, but he is young and has to work a lot. He is very smart and knows he has a lot to improve.
"We have a lot of faith in him and he has won us over thanks to his humility and work ethic. It's easy for people to fall in love with him. He trained today in front of 57,000 people. He is a great player."