Eben Etzebeth will miss the first three rounds of Vodacom Super Rugby because of a chest injury.
The Stormers lock left the field in the first half of the pre-season game against the Cheetahs at Newlands on Friday.
At the post-match press conference, Stormers coach Allister Coetzee said he would wait to see the results of the scans, which have proven worse than initially feared. In addition to the Stormers' opening match against the Bulls at Loftus, Etzebeth is set to miss the home game against the Blues and the trip to Ellis Park to face the Lions.
Etzebeth's absence is further compounded by the news that Argentinian lock Manuel Carizza is expected to spend the next three weeks on the sidelines.
Meanwhile, Damian de Allende is still struggling with a quadricep injury and will not be risked for Saturday's match against Boland at Cape Town Stadium. The Stormers have chosen to take similar precautionary measures with loose forwards Siya Kolisi (tight hamstring) and Nizaam Carr (viral infection).
All three are expected to return for the match against the Bulls, along with Kobus van Wyk, who misses out this weekend with a minor calf strain.
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