He will be out for between eight and 10 weeks, according to a brief statement from the Bulls, and might need surgery after consulting doctors.
The 23-year-old returned at the start of the Super Rugby season in February, having missed the 2016 campaign after rupturing knee ligaments in a freak training ground accident.
Pollard, regarded as one of the most exciting Springbok prospects in years, also suffered complications after elective shoulder surgery, adding five weeks to his hospital stay.
He won his first South Africa cap aged 20 and has played 20 tests, the last at the 2015 Rugby World Cup in England.
Pollard was expected to be first-choice flyhalf for the Boks this year after they had a miserable 2016 campaign without him.
(Reporting by Mark Gleeson in Cape Town; Editing by David Goodman)
