The mercurial talent rounded his defender and was well over the try line when the Cardiff player ankle-tapped him in the Stormers' 44-21 United Rugby Championship quarterfinal victory in Cape Town on Saturday.
The 24-year-old was in immediate pain and went off the field shortly afterwards. Feinberg-Mngomezulu was last seen going down the tunnel on crutches at the end of the match. He then confirmed he was set for a spell on the sidelines with a lengthy post on Instagram late on Sunday.
"Usually, I post caption-less carousels. This time I'll say it how it is," Feinberg-Mngomezulu captioned.
"Frustrated, irritated and questioning why me? First time injured in 14 months. Sometimes the game reminds you that you're not invincible! 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!!"
According to reports, scans confirmed a syndesmosis (high ankle) injury, which usually requires three months of recovery.
The Bok No.10 looks set to miss the initial part of the international window, where the Springboks host England, Scotland and Wales in the inaugural Nations Championship in July. Following that, Feinberg-Mngomezulu is in a race against time to be fit for the highly anticipated Rugby's Greatest Rivalry Tour against the All Blacks.
The more immediate concern is for the Stormers, who have the unenviable task of travelling to Dublin to face Leinster in the URC semifinals this week without their playmaker.