Springbok No 8 Duane Vermeulen, man-of-the-match in the 2019 World Cup final, is now an injury concern ahead of next month's series opener against the British & Irish Lions in Cape Town.
This comes after the 34-year-old, considered one of his country's strongest rugby weapons, limped off in the 33rd minute of Friday night's Rainbow Cup clash between the Bulls and the Stormers at Loftus.
The Bulls won the match 31-27.
The footage that followed showed Vermeulen with his left ankle on ice, and while further clarity will be provided in the days ahead, early indications are that the injury will be a worry for Bok coach Jacques Nienaber.
"It doesn't look too good, I must say," Bulls coach Jake White said of his captain after the match.
"He's a tough guy and for him to say he wants to come off is not ideal. We know that if he says he's sore, then it means something.
"He said he was feeling a bit sore."
White revealed that Vermeulen had hurt the same ankle with a "different injury" and "a couple of weeks ago."
"He's obviously got ambitions of being involved in the Springbok side and playing against the Lions," White said.
"I'm hoping for his sake that it's just a minor twist in his ankle."
Stormers scrumhalf Herschel Jantjies, meanwhile, also left the field in the first half but coach John Dobson confirmed after the match that he had fallen ill in the hours leading up to kick-off.
The first Test between the Boks and the Lions takes place on 24 July.