MANCHESTER -- Jose Mourinho has revealed that signing a replacement for Michael Carrick is Manchester United's top priority this summer.

The midfielder, who turned 36 in July, is set to hang up his boots at the end of the season and join Mourinho's coaching staff.

And the United manager says that, after "completing" his attacking options with the signing of Alexis Sanchez from Arsenal, his focus is on bolstering the midfield ahead of next season.

He told a news conference on Monday: "I think in attack it's difficult for us to improve. Where are we going to get a better combination of players than we have? "We cannot buy [Lionel] Messi and Cristiano [Ronaldo] -- these are the best players of the last decade.

"Where can we get better players than [Juan] Mata, [Anthony] Martial, [Jesse] Lingard, [Marcus] Rashford, Alexis [Sanchez], [Romelu] Lukaku? In attack we have an amazing group of players.

Michael Carrick is set to retire at the end of this season. AFP PHOTO / Paul ELLIS

"In midfield Michael Carrick will not be No. 16 next season, so we lose a player. It's there in midfield where we need to -- I'm not saying improve -- but we need to get a player to compensate the situation of Michael."

Sources have told ESPN FC that Man United hold an interest in Nice midfielder Jean Michael Seri while Napoli's Jorginho has also been linked with a move to Old Trafford.

Mourinho is also still waiting to learn if Marouane Fellaini will sign a new contract or leave for free in the summer.

And he admits that if the Belgian heads for the exit, he may be forced to sign more than one central midfielder.

He added: "If Marouane leaves, yes we have two gaps there, so let's see what happens. The good thing is that he would like to stay with us and we would like him to stay with us. To sign a contract a person must be happy. Let's see if we can make him happy."