The midfielder has struggled for minutes this season.
Mourinho said on Sport TV, "For me it is never a problem, but a solution.
"Having him in the squad, even if he is not called up and not playing, is an extremely comfortable situation. I will never be the one to push him or say that I don't want him here.
"But I understand the situation of the kid and Benfica. If the club wants to end the relationship here, we will be here to collaborate, because we want the good of the player.
"Benfica has the power to decide and will be accepted by us."
On Carlos Vinicius, also on-loan from Benfica, Mourinho continued: "Vinícius is different. He arrived and his space is obvious. We have two strikers, we don't have three, four or five, and he is one of the two. The other is one of the three best strikers in the world and that creates a difficult situation, but they can play both together, there are games in which they will do it.
"Alternation is important because Harry cannot play all games. Vinícius will play many times, he will have the opportunity to prove in the Premier League and convince Tottenham to buy him. If he doesn't, he will return to Benfica a lot richer and a lot more experienced. This operation is good for the three parties."