Monaco have reportedly informed interested clubs that central defender Benoit Badiashile will not be allowed to leave the club this summer for anything under €50m (£42m).
Chelsea appear to have lost out to Barcelona in the race to sign Jules Kounde from Sevilla, which could see the Blues switch their attention to long-term target Badiashile before the end of the window.
Manchester United, meanwhile, have agreed a deal to sign Lisandro Martinez from Ajax this summer, but Axel Tuanzebe, Eric Bailly and Phil Jones could all leave Old Trafford before the end of the transfer window, so a move for another centre-back has not been ruled out.
According to L'Equipe, Chelsea, Man United and Barcelona are all admirers of Badiashile, who has spent the last four seasons in the first team at Monaco.
The report claims that Sevilla have also expressed an interest in the centre-back as a replacement for Kounde, but the Ligue 1 side have made it clear that they will not accept offers of less than €50m (£42m).
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The 21-year-old joined Monaco in 2016, signing his first professional contract in early 2018 before making his first-team debut towards the end of the year.
The France Under-21s international has since represented the Ligue 1 outfit on 119 occasions in all competitions, contributing four goals and three assists in the process.
Last term, the defender made 34 appearances for Monaco, scoring once and providing four assists, with 24 of those outings coming in France's top flight.
Badiashile only has a contract with the principality outfit until 2024, and there are not believed to be any concrete talks at this stage over a possible extension.
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Barcelona would be unlikely to move for the defender if they managed to sign Kounde from Sevilla, but Chelsea will sign at least one more centre-back before the end of the transfer window.
Meanwhile, departures for Bailly, Jones and Tuanzebe would open up space in the squad at Old Trafford for another defender, but Man United are also still working on deals for Ajax's Antony and Barcelona's Frenkie de Jong.
Monaco have already made big money this summer by selling Aurelien Tchouameni to Real Madrid, so the club are in a strong position to demand a high transfer fee for Badiashile.
Wissam Ben Yedder, who has scored 73 times over the last three seasons for the Ligue 1 side, has also been linked with a summer exit.
Man United are believed to be interested in the striker as a replacement for Cristiano Ronaldo, who could yet force a move away from the 20-time English champions before the end of the transfer window.