Casemiro has been a shining light for Real Madrid this season with a string of fine performances in midfield.
However, according to Spanish outlet Don Balon, the Brazilian’s stock has risen so much that a number of European heavyweights are willing to pay a top price for his services.
Real skipper Sergio Ramos has apparently discovered the interest from overseas and has alerted bosses at the Bernabeu.
Jose Mourinho knows Casemiro from their brief encounter in 2013 when he was boss of Real.
The holding midfielder was on loan from Sao Paulo to Real Madrid B before his transfer was made permanent later that year.
The Manchester United boss is looking to strengthen the middle of the park after Michael Carrick retired and Marouane Fellaini refused to sign a new deal.
But Don Balon say the Portuguese manager faces three dilemmas.
The first is that PSG are Casemiro’s most favourable side to join, should he leave the Bernabeu, because he could link up with fellow countryman Neymar.
Serve A giants Juventus also pose another problem should they act on their interest.
But finally Real president Florentino Perez is said to be keen to sit down with the 26-year-old try and convince him to stay in the Spanish capital.
Casemiro has recently revealed his love of working under Mourinho.
“[He told me] ‘I know you, you are good, and you are going to be the best central midfielder in the world’,” said Casemiro.
“He gave me this confidence, I left the dressing room believing that I was Cristiano Ronaldo.
“With the energy that he gave me, I was left believing that he was the best in the world.
“The confidence and energy that he gave me was incredible.”