The former United winger has revived his career since leaving for Olympique Lyon last year.
And as part of the transfer, Mourinho insisted on the inclusion of a buy-back clause.
He said, "Potentially, he is a very good player. When Mr Van Gaal (former manager of United) decided to buy him, he did well.
"He did not succeed in 18 months but he is very young so I think it's very important for the club to have total control of his talent and we all wish him to play very well in Lyon and why not come back because everyone here likes him."