The United boss sent scouts to watch the 29-year-old recently in the Champions League against Atletico Madrid.

He is a huge admirer of the Belgian midfielder as sees him as the perfect fit to replace Michael Carrick next summer.

Mourinho also watched Atletico's Antoine Griezmann and £85m-rated Saul Niguez, who he is a long-time fan of, during the match.

United are still hopeful of landing the French striker next summer after a number of failed bids in the last window.

The Red Devils are understood to be lining up an £88m bid for the 26-year-old.

An Old Trafford source said: “Jose sent scouts to the game to look at a number of players, but most importantly Nainggolan.