De Bruyne has only started two Premier League games since joining the London club two years ago and has had loan spells at Genk and Werder Bremen.
And his agent said earlier this week that the 22-year-old was eager to impress ahead of the World Cup in the summer and was therefore hoping for a permanent move in the transfer window.
But Mourinho said: "This is the period for agents to be famous.
"We know Kevin didn't adapt very well to the difficult life a Chelsea player has, which is to pay a big price to play.
"They have to give a lot, to work a lot, and to accept competitiveness. This is the first time he came to a big club with big competition.
"He is a fantastic player with fantastic potential. I don't want him to leave but we have a couple of contacts made by other clubs.
"But, if people think they can get our good players on sale, the sales finished in London yesterday."
Chelsea to field strong side at Derby
Mourinho was speaking ahead of Sunday's FA Cup third-round tie at Derby and plans to field a strong starting line-up at Pride Park, although there may be a change in goal.
"My squad is the same," he said. "We go with the best possible team to try to win the game.
"We go to win with our best team but, if we think Petr (Cech) needs a rest, for Mark (Schwarzer) to play is not a problem.
"We are not going to give a break to some players because we want to win the game, and we don't want to play a second game.
"The FA Cup has a special feeling, a special meaning. To win the FA Cup at Wembley was one of my high moments."