Bayindir, 28, travelled to the World Cup with Turkey but did not feature in any of their three group games, with the side failing to progress to the knockout stage. Their campaign ended on June 26 with a win over the United States.
Having already completed his mandatory three-week break, Bayindir is not due back at United's Carrington training complex this week, along with team-mate Amad. Fellow World Cup traveller Tyler Fletcher, by contrast, reported for pre-season last week having been an unused substitute throughout Scotland's tournament.
Amad enjoyed a considerably more eventful summer on the pitch, playing in all four of Ivory Coast's matches and scoring the winner against Ecuador before netting again in their round-of-32 exit to Norway.
For Bayindir, the extended absence fits a summer in which his Old Trafford future has looked increasingly uncertain. The former Fenerbahce goalkeeper is expected to return to Turkey, with a move to Besiktas the most persistent link, and personal terms are understood to already be in place between the player and the Super Lig club.
He has not featured for United since a mistake-strewn appearance in their 3-1 defeat at Brentford in late September, a display that hardened the club's determination to move on from him. United lost seven of the 17 Premier League games he started, conceding 31 goals across that run, numbers that have left Bayindir firmly behind Senne Lammens in the pecking order.
With United keen to trim their goalkeeping department and Besiktas continuing to push for a deal, Bayindir's homecoming now looks to be a matter of when rather than if, even if the final terms between the two clubs are still being finalised before pre-season gets fully under way.
Manchester United signed Bayindir from Fenerbahce in 2023 in a deal worth £4.3million, and while he has never nailed down the number one role at Old Trafford, a fee recouped now would still represent useful business as the club looks to fund fresh investment elsewhere in the squad this summer.