Reports have claimed a deal in the region of £40 million is close to being agreed between the two clubs for the 28-year-old Serbia international midfielder.
Matic would be United's third summer signing following the arrivals of defender Victor Lindelof from Benfica and striker Romelu Lukaku from Everton. It would also be the second time Mourinho has bought Matic, having signed him for Chelsea in 2014.
Asked about the possibility of a reunion following United's 3-0 pre-season friendly win against Valerenga in Oslo on Sunday (30.07.17), Mourinho said in a press conference shown on MUTV: "I'm waiting for news. I know that he wants that very, very much and when a player wants very, very much the chance is bigger, the chance is bigger, so I think we have a chance but in football until it's official, I saw so many things happen that I refuse to say more than I am telling you now."
Chelsea spent £21 million just over three and a half years ago to buy Matic from Benfica for a second spell at Stamford Bridge, but he could be heading for the exit door from the London club once again.