Mourinho appeared to pave the way for Mata's departure after the player's frustrated reaction to being substituted during the New Year's Day win at Southampton.
Mata, the club's player of the year for the last two seasons, has struggled to establish himself as a first-choice selection since the Portuguese tactician returned to the club during the close season and has been linked with a move to Manchester United.
And the manager's claim that the club's "door was open" if the player wanted to discuss a move away was taken as an indication that Mata's days at the club are numbered. But Mourinho declared himself happy with the way Mata has reacted to the latest disappointment.
Speaking on Friday ahead of Chelsea's FA Cup third round trip to Derby County, the manager said: "He's not been in to see us and today he trained in a fantastic way.
"He focused more on what I said after the game, when I said 'I don't want him to leave'. He focused on that rather than 'the door is always open'. When he focuses on me not wanting him to leave, he moves on, he was happy with the victory and trained fantastically, no problems."
Mourinho refuted suggestions there had been interest in the Spaniard from United, saying: "There has been no interest from other clubs. I keep saying I want him to stay. There is no other offer, no offer."
Mourinho squashes other transfer rumours
Mourinho also denied negotiations are underway that will see Belgian international Kevin De Bruyne leave Chelsea to join Bundesliga club Wolfsburg.
But he admitted the player has struggled to adapt to life at Stamford Bridge while insisting he would not be allowed to leave on the cheap. "We know that Kevin didn't adapt very well to the difficult life a Chelsea player has," he said.
"People like Oscar, Mata, Willian, (Eden) Hazard have a beautiful, difficult life. To play they have to pay a big price, work a lot, give a lot, accept this difference. Kevin has a different personality. He was a very important player for Genk (and Werder) Bremen.
"This is the first time he has come to a big club with big competition. He's a fantastic player with potential but it is difficult to adapt to this situation.
"We know he fancies a move but he's a fantastic player, so is very expensive. When you buy fantastic players you have to pay a lot for them. If people think they can get good players on sale, the sales finished in London yesterday!
"I don't want him to leave. But we have a couple of contacts, not made by us but other clubs. I don't know if he'll go. We don't want to sell."
Turning his attentions to the FA Cup, Mourinho said he will field a strong team against Championship side Derby and disagreed with the view of Aston Villa manager Paul Lambert, who described the competition as an unwanted distraction this week.
Mourinho said: "I don't agree with Paul Lambert. He has the right to express his opinion and think differently to me. I have the same right. Especially for teams without European competition, where FA Cup matches come in a normal weekend, I don't see a reason for clubs to not try to win it.
"Even for the smallest clubs, it is maybe difficult to reach the final but the FA Cup has a special feeling and meaning. I won lots of trophies but to win the FA Cup at Wembley and feel what that means was one of the high moments in my career.
"I have a good feeling for the competition and the good things this country has in terms of football. I think we have to keep them."