Kean, who joined the Blues from the Italian champions this summer, has had a slow start to the season, failing to score in any of his opening five games in an Everton shirt.
But Mourinho says: “I am excited, I think he can score a goal. We are talking about issues, stability in performance, with that.
“Is he able to do that, is he capable of doing that. Does he have the personality to do that? Is that the reason Juventus sold him or not? We don't know."
Mourinho has expressed his bewilderment at the Old Lady's willingness to sell the forward, who has three caps for Italy.
“I am a little surprised," he said. “Last season he showed, at least for us, from our perspective, watching from our side of the screen, he showed qualities as a player but also this no fear to come into a Juventus team full of stars and score goals.
“Then, something that I put some question marks as to why Juventus sell, when they have strikers of top quality, like [Cristiano] Ronaldo, like [Mario] Mandzukic, like [Gonzalo] Higuain, who are over 30 years old, they sell a striker that I recognised potential.
“To sell him such a young striker, why? If I find [Pavel] Nedved (former Juventus player and vice-chairman) around the corner, I would ask him, why did you sell him? Then probably I would understand."