Stormers back Gio Aplon is expected to be out for six to eight weeks after dislocating his elbow in the loss to the Reds.
The Springbok sustained the injury when putting his arm out after a tackle from Reds prop James Slipper.
The good news for the Aplon and the Stormers is that there was no fracture, which would have prolonged his time on the sidelines even further.
"Gio dislocated his left elbow and, at this stage, it seems that he will be out of action for six to eight weeks," said Coetzee.
"It's obviously a blow to lose someone of his ability and experience, but one bit of solace is that it's not a fracture.
Top 14 side Grenoble announced the signing of Aplon last week.