Bulls forward Deon Stegmann has been ruled out for nine weeks, the second Springbok after Handré Pollard to be ruled out.
The experienced back-row has been sidelined with an ankle injury.
Both players would have been instrumental in the first weeks of Super Rugby for the Bulls. Pollard's knee injury will re-assessed in two weeks' time.
The Eastern Cape-born Stegmann has been burdened with injuries – in the 2015 Currie Cup season he was sidelined for four weeks with a fractured cheekbone.
Roelof Smit will however return to the squad after recovering from a prolonged wrist injury and he should provide adequate back-up for the former Cheetah.
The final squad for the Bulls pre-season tour is set to be announced within the next few days.