"He's here and he works hard. He knows that I know he is a good player and he has space in the squad. Until August 31 the market is open for every one of my players that is not happy, but to be fair I think he is (happy)," Mourinho told the BBC.
"I think he is happy and I am not expecting him to ask to leave. I am expecting him to do what he is doing now, which is to fight for a place."
"We have 38 matches in the Premier League, we expect to play a lot of them in the Europa League and domestic cups so in a squad of, let's say, 22 players, there will be a space for everyone. So, yes, there is a space for Juan," Mourinho added.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Mata scored six goals in 38 Premier League appearances last season as United finished fifth in the standings.
Since his arrival in May, Mourinho has boosted United's squad by signing defender Eric Bailly, midfielder Henrikh Mkhitaryan and striker Zlatan Ibrahimovic and, according to media reports, is chasing midfielder Paul Pogba from Serie A champions Juventus.
The 53-year-old refused to comment on the Frenchman's possible return to United, but said he has three different choices for his final major transfer.
Mourinho's first game in charge will be against Bundesliga side Borussia Dortmund in the International Champions Cup in Shanghai later on Friday.
(Reporting by Ian Rodricks in Bengaluru; Editing by Amlan Chakraborty)
