Bulls scrumhalf Piet van Zyl picked up a knee injury in his team's 12-19 Super Rugby loss to the Waratahs at the weekend.
Van Zyl, who left the field in Sydney on the half-hour mark, will not play against the Western Force in Perth on Saturday - the last tour match of the Bulls' Australasian trip.
Van Zyl will be sidelined for two weeks, according to Bulls team doctor Org Strauss.
Good news is that both Akona Ndungane (knee) and Jurgen Visser (foot) have been declared fit to face the Force in Perth.
Ndungane's availability will result in Francois Hougaard moving back to No.9, at the base of the scrum.
The Bulls are also awaiting the result of Flip van der Merwe's citing, as this will determine his availability for the match.