Stormers head coach Allister Coetzee has confirmed that eighthman Nizaam Carr will be out for the season.
The former Bishops star injured his knee at a first-half ruck in Saturday's bruising 16-14 win over the Cheetahs at Newlands.
Carr was replaced by substitute Jebb Sinclair, the Canadian and London Irish player, who joined the Stormers last week.
Coetzee said it is likely that Sinclair will be promoted to the run-on XV next week against the Waratahs.
The Bulls went top of the overall standings following their last minute 27-24 win over the Waratahs in Sydney
The Chiefs are a point adrift of the Bulls in second place but still top the New Zealand conference after losing 42-27 to the Reds in Brisbane on Sunday.
The Sharks demolished the Force 53-11 in Durban while the Lions lost the battle of the basement clubs, 25-3 to the Blues in Auckland.
The Rebels were notable 28-19 winners over the Crusaders in Melbourne.
