Fourie lasted only moments after coming off the bench midway through the second half before being helped off the field. He was later seen on crutches with his leg in a moonboot, casting doubt over his playing future.
Stormers coach John Dobson admitted they were "at a crossroads" with the 38-year-old flanker and hooker due to the suspected severity of the injury and his advanced age.
"That's a very serious injury, by the looks of things," Dobson said after the match. "It looks like a broken tibia. We haven't scanned or x-rayed him yet... but Keke [Morabe] was out for close to a year with that.
"You'd have to do the maths and realise we're probably at a crossroads, which I hope is not the case.
"Often with those things, it depends on the nature of the break."
Fourie was named in the Springboks' first alignment camp of 2025 in March despite not playing for the Boks last year due to injury. He played a vital role in their 2023 World Cup victory and was still considered a valuable back-up option.
He spent months on the sidelines in 2024, missing the entire Bok season, after a knee injury sustained in a Champions Cup clash against La Rochelle in April 2024, only returning to action in late December.
Dobson added: "You'll remember last year after La Rochelle, he said, 'I'm not finishing my career in a golf cart'. Knowing Deon, he's not going to want to finish it like that. Let's hope."