The midfielder penned new terms to 2024 today.
"I'm really happy," Mourinho said. "Everybody in the club is, his team-mates are, I am and Skippy is or not he wouldn't sign the contract. I think he's genuinely Tottenham's future.
"He's one of these players by human quality, by personality, he is one of these kids that I have no doubt he will be an important player for Tottenham.
"Sometimes coaches are selfish and I told him that. I never told him I want him to go on loan, I always told him I wanted him to stay here because that's the selfish perspective of a coach who wants the best possible squad.
"In his mind he wants to go on loan, [for] six months, the whole season. He feels that he needs that, I also feel that would be good for his evolution, so maybe that is the direction we go. I think he can be more than a player, he can be a future captain here. Hugo, Harry.
"I see this kid being one day a future captain here by his character, by his personality. I feel really happy that he signed."