Sunderland have terminated Papy Djilobodji’s contract after the League one Club said the Senegal centre-half waited until this month before reporting back for “pre-season” training and then failed a fitness test.

By sacking the 29-year-old former Chelsea defender, who cost £8m two years ago, Sunderland will be unable to recoup a transfer fee but Stewart Donald, the chairman, has said he is taking legal advice about the possibility of the club potentially suing  Djilobodji and Didier Ndong on the alleged grounds of “deliberately devaluing themselves”. It is understood the decision to tear up the former’s contract does not preclude the possibility of such a move.

Ndong, a Gabon midfielder who became the club’s record signing at £13.6m when he signed from Lorient of France in 2016 at a time when Sunderland were in the Premier League, is said to be awol and Donald says the club do not know where the 24-year-old is. Ndong, who did not return to training in July, recently posted Instagram pictures of himself relaxing by a swimming pool which have since been deleted.

“In order to facilitate that desire, the club entered into a written agreement with the player allowing him to spend the month of July on voluntary unpaid leave. When that period came to an end, the player was expected either to leave for a new club – having reached a deal satisfactory to himself and SAFC – or to return in shape to play professional football. Instead, he returned to Sunderland over a month later, in the first week of September, ignoring written requests for his return. On his return, he was subjected to the same fitness test that his fellow professionals had undertaken on their return. He comprehensively failed that test.

“As a result, Sunderland AFC can confirm that it has accepted Papy Djilobodji’s repudiatory breaches of contract and notice of the same has been provided to the player.”

The failure of Djilobodji and Ndong to report for duty at the League One club is suspected by Sunderland to have been informed by a mutually cynical desire to force down their value to the point where Sunderland would either terminate their contracts, leaving them free agents, or sell them for minimal fees. If true, this could have enabled both players to command higher wages than they could otherwise expect at new clubs and would explains why the duo stayed away despite Sunderland withholding their wages.

Djilobodji – who spent last season on loan at Dijon – was earning around £32,000 a week at Sunderland and Ndong – who spent the second part of last season on loan at Watford but did not play a minute of first-team football – commanded about £25,000 a week.

“The question is whether they’ve done enough in breach of their contracts [for us] to terminate their contracts and pursue them for wilfully devaluing themselves,” said Donald on Tuesday. “Didier Ndong has shown no interest in returning to the football club whatsoever – we don’t even know where he is.”

Ndong turned down a prospective £6.6m move to Torino in June because the Italian club could not meet his wage demands.

Neither of the players nor their representatives were contactable.