The Portuguese boss will leave Real Madrid at the end of the season and is widely expected to return to Stamford Bridge for a second spell as Chelsea boss.
"Jose is one of the best," World Cup and Euro 2012 winner Mata told reporters on Chelsea's United States post-season tour. "He won everything in every country he was - in Portugal, in Italy, in Chelsea in London. We don't know really what is going to happen but if he comes he is welcome because he is one of the best and Chelsea always want to be a top side."
Mata added: "If he comes we are going to be happy to have him."
Mourinho led Chelsea to two Barclays Premier League titles during his first spell in charge, from July 2004 to September 2007, including the Blues' first championship in 50 years.
Mata has won the Champions League, FA Cup and Europa League with Chelsea, but is keen to win the domestic title.
Mata added: "If he comes we will try and do our best with him, or whoever, to win the title, because one challenge for me will be to win the Premier League."