The midfielder has been linked with a move away from the Premier League club having been left out by Mourinho for the last two matches, but the manager revealed that he is "tired" of questions about Alli.
The 24-year-old has been included in the Tottenham squad for their Europa League qualifier against North Macedonian side Shkendija.
Mourinho said: "He is coming and he has a chance to play. It's important for him to perform.
"When the squad becomes competitive, the players have to have an answer and perform."
The Portuguese coach added that improvements that need to be made are mostly Alli's responsibility.
He explained: "I am not tired of Dele because he is a great kid, but I am tired of questions on Dele.
"I always feel that 99 per cent of the responsibility is the player. I have 1 per cent. Me and my staff and the people that work, everybody has 1 per cent."
Alli's teammate Harry Winks feels that he will regain his form.
He said: "Dele is a top player - you don't get to the level he has got through luck.
"You get there through hard work and ability. It might be a dip in confidence, I don't know what the situation is but he is a top pro.
"Everyone in the team will back me in saying that he will get back to his best form and he will do."