The Serbian international completed his United medical on Sunday ahead of his potential move to Manchester. The Red Devils have managed to beat Juventus in securing the 28-year-old's signature.
Matic's desire to join United in the summer transfer window saw the Italian champions and Champions League finalists end their interest in the Blues star. This has given the 20-time English champions the edge in completing the midfielder's transfer.
"I'm waiting for news. 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," Mourinho explained, as quoted by the Manchester Evening News.
"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."
Matic was spotted in United's training kit and the picture was widely circulated on several social media platforms. He sported number 31, leading to the suggestion that the Serbian will be taking up the number that was vacated by Bastian Schweinsteiger following his switch to Chicago Fire earlier in March.
When asked about the number 31, Mourinho explained: "I don't know because I was not there [at United's Carrington training complex]. I don't know. I really don't know. Number 31 is a free number. It was Schweinsteiger. It's a free jersey, we have a few free and 31 is one of them."
The Red Devils have completed two signings so far this summer. Victor Lindelof swapped Benfica for United, while Romelu Lukaku left Everton to reunite with Mourinho at Old Trafford. The Belgium international worked with the Portuguese tactician at Chelsea in the past.
Matic's imminent arrival will see him become United's third signing of the summer transfer window.
Meanwhile, United finished their penultimate pre-season fixture with a 3-0 victory over Valerenga in Oslo on 30 July. Marouane Fellaini opened the scoring before the break and Lukaku, who came off the bench at the start of the second half, doubled the lead.
It was the 24-year-old's third goal of the pre-season with his new club. Mourinho has explained why Lukaku's goals in the friendly fixtures are no longer important for him.
"It's nice. You know strikers, they like to score goals. It's not important for me but probably it's important for him. It's important for his confidence and for his self-esteem," the United manager was quoted as saying by the club's official website.
"Strikers like to score goals; us managers, many times we are happy with them even when they don't score, because of the way they participate in the team organisation and game plans. But, for them, to score their goals is always important."