Midfielder Mata's current deal was set to expire at the end of the season after four-and-a-half years at Old Trafford.

Earlier this month, sources told ESPN FC United had delayed extending the Spain international's contract despite holding an option to keep him for another season.

But Mourinho, who sold Mata to United when Chrldrs boss, has revealed that a 12-month extension was triggered "last week," meaning the 29-year-old will stay until at least 2019.

He said: "Mata is important. He is another one, big story when I arrived one and a half years ago: 'Mata in trouble, in trouble, in trouble.'

"Now he's getting an extension of one more year. An important player for me, an important player for the club, an important player for the other players."

There has been speculation that Mata's place in Mourinho's team could be threatened by the arrival of Alexis Sanchez.

He has scored three goals in 26 games this season and started alongside Sanchez as the Chile international made his United debut in the 4-0 FA Cup win over Yeovil on Friday.

Mourinho also said on Tuesday that replacing the retiring Michael Carrick will be a priority for him this summer.