Atletico Madrid have contacted Chelsea over defender Toby Alderweireld.
The 26-year-old spent last season on loan in the Premier League with Southampton.
Ronald Koeman’s Saints retain an option to purchase the player for close to £7million but Madrid can scupper those plans by paying a £1.5million fee to remove the clause.
Tottenham and Manchester City are also believed to be interested in signing the Belgian international but the Blues would be favourites if Jose Mourinho decides to pursue the negotiations.
Alderweireld said recently: “I really want to go to a club that really wants me.
“There are three options - stay with Atlético, stay with Southampton or go to another club. So we will see what happens.
“Southampton gave me that opportunity and it paid off, I think. I’ve had a fantastic year, I can’t lie about that, so, yes, I’d like to stay in the Premier League."
Chelsea have a good relationship with Atletico having previously loaned Thibaut Courtois to the La Liga outfit and taken Diego Costa and Filipe Luis from the Vicente Calderon.
Costa has been a big hit since making the switch, although recent reports suggest he is unsettled in England, while Luis has struggled to break into Mourinho’s first-team plans.
The Brazilian full-back could be used as a makeweight if the Blues also decide to push further for Alderweireld’s Atleti team-mate Antoine Griezmann, who has a £43.5million buy-out clause.