Spanish news provider Don Balon report that Manchester United scouts are monitoring Real Madrid's Raphael Varane, Alvaro Morata and James Rodriguez.
The publication say that Jose Mourinho is a big admirer of the three stars and that scouts will be watching with interest when Madrid take on Atletico Madrid in the second leg of the UEFA Champions League semi-final on 10 May.
In addition, Atletico's Antoine Griezmann is said to be linked with the side and he will also no doubt be under the spotlight at the Vicente Calderon Stadium.
Varane played the full 90 minutes in the first leg and helped keep a clean sheet at the Santiago Bernabeu, as the Zinedine Zidane-coached outfit triumphed 3-0.
However, Morata and Rodriguez were left on the bench and Don Balon report that their lack of playing time this season means they could be open to a move to Old Trafford.
The Red Devils are looking to improve their squad as they look to challenge for the Premier League title, something they haven't managed since Sir Alex Ferguson retired.