The United boss refused to name names yesterday but made it clear that he only wants players who can bring success to Old Trafford.
United haven’t won the title since Sir Alex Ferguson retired in 2013.
But Mourinho believes some of his players are too content to drift in the comfort zone.
Anthony Martial, Luke Shaw, Jesse Lingard and Chris Smalling have all fallen out of favour this season.
“Play to win, responsibility to win, cope with the pressure to win,” said Mourinho. “This is something that has to belong to your natural habitat. For some guys, it doesn’t.
“They also need that time to go out of their comfort zone or a zone where they are protected that we assume the objective is not to win.”
United are unbeaten in 14 Premier League matches – a run stretching back to October 23 – as they prepare for tomorrow’s trip to Leicester.
But seven of the games in that run were draws, including each of their last three, against Liverpool, Stoke and struggling Hull.
No team has drawn more than United’s nine in the league, the chief reason that they start the weekend in sixth place, 14 points behind leaders Chelsea.
But even though the Premier League title is realistically out of reach this season, Mourinho has no regrets about declaring his ambition to make United champions again.
He said: “I was speaking about being champions because I don’t think there is another position that a manager can have at this club.
“It would be easy for me to say that we want to play better, that we want to improve the quality of my game, that we want to improve the relationship between the players and the fans.
“And I do want the fans to feel again more connected with the team and style of play.”
Mourinho has admitted that United have to improve their scoring record, having managed only 33 Premier League goals this season – 15 fewer than Chelsea and 19 behind top scorers Liverpool.
But he insists that their style of attacking play has deserved more goals, and suggested that his Premier League rivals are getting more credit for their forward play despite being less attacking in a dig at former club Chelsea.
He said: “There are teams that are very defensive, and with the first shot, they score, and the second shot, they score, and then you chase the goals and the power of the numbers, and you say that the team is magnificent.
“With us it’s the opposite. We always play, we always try to score and to try to win. And yes, it’s true, since October, we haven’t lost a match in the Premier League.
"That’s a lot, that’s three months, but we should score more goals and win more matches.”
