Mabokgwane was recalled to Sundowns and offered an extension on his contract after spending last season with Platinum Stars.
But the former national Under-20 goalkeeper is in Johannesburg training on his own.
Sundowns PRO Kabelo Mosito tells KickOff.com that Mabokgwane is not part of the club's pre-season training.
"Yes, it's true that Jackson is not part of the team that is in Swaziland for the pre-season training.
“This is a technical team decision and I wouldn't be in good position to give further information about him with the team and technical team still in Swaziland," he adds.
Sundowns have already sent defender Ramahlwe Mphahlele to train with the club's development after Neeskens announced that he was not part of his plans together with Buhle Mkhwanazi.