Jose Fonte's contract talks with Southampton have broken down and he could leave the club in January, sources close to the player have confirmed to ESPN FC.
Southampton have been in talks with Fonte over a new deal since the summer but they have been unable to agree terms with the club captain.
Fonte is entering the final 18 months of his contract at Southampton and, with the player turning down the Saints' offer to extend his deal, the club are reluctantly willing to sell him in January if they receive a suitable offer, sources said.
However, after many news outlets reported talks had stalled, Fonte on Tuesday responded to a Southampton fan Instagram post about the reports by saying it was "Not true at all!!!"
The 32-year-old, who helped Portugal win the European Championship in the summer, was a target for Manchester United and Everton in the summer transfer window.
United boss Jose Mourinho had sought to bring in a defender with Fonte's profile in the summer and is a big admirer of his compatriot.
He remains keen to add to his centre-back options in January and United have been linked with a host of names, including Benfica's Victor Lindelof, but the Portuguese giants have placed a £40 million price tag on him, which may prohibit a move.
Everton chief Ronald Koeman is also looking to shore up his defence, and he has previously worked with Fonte during his time in charge of Southampton.