Feinberg-Mngomezulu took to social media on Sunday to comment on the injury, which came as he scored a second-half try. He received an ankle tap and appeared to twist his left ankle in the process.
Stormers coach John Dobson said after the game that the injury looked “serious” and suggested it might be a ligament issue.
“Frustrated, irritated and questioning why me? First time injured in 14 months. Sometimes the game reminds you that you’re not invincible!” Feinberg-Mngomezulu said on Instagram.
“Another injury, another chance to come back hungry, determined and focused. I’ve got a job to do, get back and get back better than I left. I’m not one to dwell, but I’ll have a little vent! Now ... BACK TO WORK! Next job, crystal-clear vision and mindset. See you soon!”
There has been no timeframe put on his recovery, but it is clear he will miss the URC semi-final against Leinster on Saturday. More worrying for Erasmus is the lengthy Springbok season that starts in July.
It is a vital campaign a year out from the 2027 Rugby World Cup, and Feinberg-Mngomezulu, if fit, is expected to play a major role in it.
The Springboks host England, Scotland and Wales in the Nations Championship in July, before four Tests against New Zealand in the Rugby’s Greatest Rivalry series and one-off meetings with Australia and Argentina.
They will head north in November for the remainder of the Nations Championship, with fixtures against Italy, France and Ireland, as well as a positional play-off.