Khumalo, together with Wandisile Letlabika, Jackson Mabokgwane and Ramahlwe Mphahlele, have been left out from the team that went to Swaziland for pre-season training.
Khumalo was signed from Swallows in 2010 and was rated one of the country's best young talents, but has not seen much game-time at Chloorkop.
Meanwhile, KickOff.com has also been told that Sundowns and Bloemfontein Celtic have failed to agree on a move for Mphahlele after it was reported previously that the two were negotiating a deal.
Mpahlele is still training with the development team and it seems that the player will be stuck at Sundowns, despite the coach saying they are not on his plans.
Celtic coach Clinton Larsen confirmed that they will not be signing Mphahlele anymore.
"We have just signed Dominic Isaacs and we won't be signing another defender," he said.