Bulls suffer Warner blow
There is also concern about flyhalf Tian Schoeman, who is struggling with a swollen knee.
However, according to the doctor, it doesn't seem too serious.
"It is unlikely he will be sidelined for more than a week," Rossouw said, adding that the No.10 will go for a scan.,
The Bulls have a bye this week and Schoeman should be available for the play-offs, which get underway on October 15.
A couple of players are returning from injury.
Ruan Steenkamp and Arno Botha will be back in training next week, ahead of the play-offs.