Mourinho will part ways with current employers Real Madrid at the end of the season and is expected to take over as Chelsea boss within the next fortnight.
|5/2||Chelsea are 5/2 with William Hill to win the Premier League next season
"Jose is one of the best," Mata said at a press conference prior to the first of two Chelsea friendlies with Manchester City in the United States.
"He's won everything in every country he was: in Portugal, in Italy, in Chelsea in London and in Spain.
"I think we don't know really what's going to happen, but if he comes, he's welcome, because he's one of the best.
"Chelsea always want to be a top squad, a top side, and I think if he comes, we're all going to be happy to have him."
Mourinho's reign in the Spanish capital came to a disappointing and trophyless end, and although Mata cannot pinpoint the reasons for los Blancos' failure under the Portuguese, he still believes Chelsea can challenge for the Premier League title under their old boss.
"I don't know. You have to be there to understand everything," Mata said. "What I know is that Madrid is a massive club with a lot of pressure behind them, and I think it shouldn't be easy.
"All I can say is that if he comes, we're going to try and do our best with him, or with whoever, to win the title."