Mahlasela joined Chiefs last week from Bloemfontein Celtic but damaged his knee in his first training session at Naturena.
According to Chiefs physiotherapist Dave Milner, the knock is similar to the one suffered by Ramahlwe Mphahlele.
Mphahlele has not played since August last year.
“His knee got into a bad position after an unlucky tackle,” Milner told the club's website.
“He’s injured a meniscus inside the knee joint. The injury is similar to the one Ramahlwe Mphahlele had.
“We did do his medicals on Wednesday and Thursday before training and he came through his tests without any problems.”
Mahlasela is due to see a specialist today.