Sunderland players Didier Ndong and Papy Djilobodji face sanctions after failing to turn up to their pre-season training session this week.
Added to this, teammate Lamina Kone has opted to stay in Wearside while the rest of the squad travel to Portugal, after having already made it clear that he no longer wants to play for the club
Sunderland director Charlie Methven said as quoted by ChronicleLive: "Papy Djilobodji and Didier Ndong were both due to return for pre-season training at Sunderland today but did not do so.
"The club will therefore begin internal disciplinary proceedings against them, and will decide what measures to take in the circumstances."
Last season, Djilobodji went on loan to French outfit Dijon whilst Ndong was loaned out to Watford for the second half of the season.
As for the upcoming season, Ndong was set to leave the club for Italian side Torino last month, but couldn't agree personal terms so the transfer failed.
Kone is also yet to find a route out of Sunderland ahead of next season. He has not travelled to Portugal, although it is not clear if it's the manager who has told him not to travel, or the player has opted not to go himself.
Sunderland will be happy to let the players go it seems but as to where, that is still to be decided, with the Sunderland owner making it clear the club will have to be properly compensated for the players' actions.