Reinach went down in the 60th minute after an awkward incident, clutching his knee and bringing the medical cart onto the field. Although he was able to walk off unaided, concern remained on the Stormers bench as the 35-year-old was seen in a brace after the match.
Head coach John Dobson was initially cautious in his post-match assessment, warning that the injury looked serious.
"He's in a brace and hasn't been scanned yet," Dobson said. "But I don't see that being a quick turnaround. It looks like a ligament, possibly medial. Hopefully it's not an ACL, but it's serious enough to keep him out for a while.
"It's going to put us under pressure," he added. "I thought Cobus played his best game in a while today. After the hernia op, he looked like he was on his comeback."
However, there has since been more encouraging news on the Reinach front.
The scrumhalf posted a photo on Monday alongside halfback partner Sacha Feinberg-Mngomezulu with the caption 'Brothers in Arms' and, more encouragingly still, a separate note reading 'Not an ACL'.
According to reports, Reinach is expected to be fit in time for the Springboks' Test window in July, suggesting the injury is not as serious as initially feared - although it remains a blow for the Stormers at a critical stage of the URC season.
Replacement scrumhalf Imad Khan helped close out the match for the Cape Town outfit over the weekend, but Reinach's absence at the business end of the season is a significant blow.
Should he also miss time for the Boks, the likes of Grant Williams, Morne van den Berg and even Faf de Klerk could come into contention in the broader Springbok picture.