De Gea has won United’s player of the year award in four of the past five seasons.
“He is a world-class player,” Mourinho said.
“He is the best goalkeeper in the world and, if our ambitions are to be a big club, to be a winning club, you need the best goalkeeper in the world – and you need also some other players the best in the world.
“In this case, we have the best goalkeeper in the world and I know that he wants to stay.
“I know that his agent is happy to do what the player wants and I also know that the board wants him to stay and they’re working on that, so hopefully sooner or later they arrive into good conclusions.”
It is understood De Gea is open to staying at the club long-term, although as yet there has been no agreement on terms and discussions continue over extending his deal beyond 2020.
His camp are mindful of the enormous salary United agreed to pay Alexis Sanchez when he joined from Arsenal in January.
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