José Mourinho has reportedly signed a pre-contract agreement to join Manchester United. The former Chelsea boss is set to pocket £15m ($21.7m) in compensation if he is not appointed by the Old Trafford club by 1 June.

Mourinho, 53, left Chelsea in December after a disastrous start to the season. Since then, he has been persistently linked with the job at United, which is currently held by his long-time friend Louis van Gaal.

According to the Spanish newspaper El País, a source from the company of Mourinho's agent Jorge Mendes confirmed the Champions League-winning coach has already signed an agreement to move to Old Trafford. However, the insider also claimed United still reserve the right to change their mind.

"If United do not sign the final contract [with Mourinho] before 1 May, they must pay £5m; if by 1 June he's still not signed, they shall pay another £10m," the report said of United's supposed interest. "May is the key, because it's the month in which the vast majority of the signings of players are closed and the plans formed."

What's more, the report claimed the clause has been included in the pre-contract because senior officials at United, such as Sir Bobby Charlton and Sir Alex Ferguson, are still not sure if Mourinho is the right man to take the club forward. It is said, too, that Real Madrid are interesting in rehiring Mourinho as a replacement for Zinedine Zidane at the Bernabeu.