Sunderland have confirmed that they have served Didier Ndong notice that they intend to terminate his contract.
A strongly-worded statement has also raised the prospect of future legal action if and when Ndong should join a new club.
The Gabon midfielder was offered the chance to leave the Black Cats this summer but could not agree terms on moves to Torino and Benfica.
He subsequently failed to report for pre-season training and the club say 'no reason was given' for that absence.
The midfielder, who became the club's record signing in 2016, was quoted in the Gabonese media last weekend as saying he hoped to return and play a part in Sunderland's promotion push.
He appeared at the Academy of Light on Monday afternoon but was given short shrift.
A Sunderland statement reads: "Sunderland AFC has given notice under its contract with Didier Ndong. The player, who was under contract with the club until June 2021, failed to return to Sunderland for pre-season training in July as scheduled, nor in the subsequent months that followed. No reason was given for his failure to report and continued absence.
"As a result, the club has accepted Didier Ndong’s repudiatory breaches of contract and notice of the same has been provided to the player. Sunderland AFC does so whilst retaining the right to pursue the player and any club he may subsequently join in relation to compensation for the value of the player."
The club also served notice to Papy Djilobodji after the defender failed to report for pre-season training as scheduled.
Neither play will be able to join a new club until January at the earliest, even if Sunderland's decision means that they do indeed become free agents.
Players whose contracts are terminated outside of the window are not able to join a new club until the window opens again.