Ulster winger Zac Ward is a doubt for the upcoming fixture at Loftus Versfeld Stadium.
The injury occurred during Saturday's Challenge Cup victory over Zebre in Parma, where he started on the left wing.
He fractured his ankle while playing in that match.
Ireland internationals Stuart McCloskey and Nick Timoney missed out on a win in Italy recently.
Ulster hope both players will be available for selection to face the Bulls.
The visitors are coming off a 56-20 Champions Cup triumph over Stade Francais.
Richie Murphy's side sit 11th in the URC table after two draws and a defeat from their opening three games.
Forward Ben Donnell, back-three player Ethan McIlroy and second row Eli Snyman will be monitored throughout the week after resuming training.