Sunderland’s chairman, Stewart Donald, has said the club’s record £13.6m signing Didier Ndong remains awol and revealed lawyers are examining whether it is possible to sue Ndong and his teammate Papy Djilobodji for allegedly deliberately devaluing themselves.

Djilobodji, an £8m former Chelsea centre-half, had permission to miss pre-season training in July but the 29-year-old failed to clock in last month and returned only last week, when tests indicated his fitness levels were significantly sub-standard.

Ndong, meanwhile, a 24-year-old Gabon international signed from Lorient of France two years ago, last week posted poolside pictures on Instagram, though they have since been deleted.

The pair’s failure to report for duty at the League One club is believed to be informed by a mutually cynical desire to force down their values to the point where Sunderland would either terminate their contracts, thereby 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 explain why the duo stayed away despite Sunderland witholding their wages.

“I’m certain we’re allowed to fine them,” Donald told Talksport on Tuesday. “But 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.

“Didier Ndong has shown no interest in returning to the football club whatsoever. We don’t even know where he is. Papy has returned but in his last conversation [before coming back] he said: ‘You’ll never see me in Sunderland again.’”

Like Ndong, though, Djilobodji has a problem – although both players’ agents strove to find them new clubs during the summer, a series of potential sales and loan moves foundered.

“Just because they can’t move now we don’t think they’ve behaved well enough for us to say, ‘All right, we’ll pay you,’” Donald added, “never mind play them, because neither of them are in condition to play.”

Initially a compromise with Dilobodji had seemed close. “We gave Papy Djilobodji permission to not be with us in July, when he said he wouldn’t turn up if we didn’t pay him, so he could find another club,” said Donald. “We gave him some guidelines to keep himself fit to make sure he was up with the pre-season standards but he didn’t turn up in August [when he was supposed to if a new club hadn’t been identified] and neither player found a new club.

“There’s an obligation on players to turn up in a condition in which you can play football, and the reality of it is that I would probably have beaten his [Djilobodji’s] stats when he returned. He was unfortunately way off what everyone else is and then didn’t turn up for the next training session. When you’ve not turned up for 72 days and missed eight games of the season, and you come up in a condition which means you’ll probably miss the next 12 games, I think that sort of says you’re not really committed.”

Caen, Hannover 96 and Bursaspor all expressed interest in Djilobodji, who spent last season on loan at Dijon with Sunderland thought to be paying two-thirds of his £32,000-a-week wages.

Torino had a £6.6m offer for the £25,000 a week Ndong accepted in June – but were unable to meet his wage demands. He had asked to leave when Sunderland were relegated from the Premier League in 2017 but failed to play a single minute of football during a loan stint at Watford during the second half of last season.

Neither player nor their representatives were contactable on Tuesday.