Garnett will be shelved for at least awhile after aggravating the injury during a Friday game against Dallas, the coach told the Celtics' official Twitter feed.
When asked if he thought Garnett's prognosis from a magnetic resonance imaging exam was "serious," Rivers replied, "If you mean that he's not going to play this year, no, I don't worry about that. Can he miss 4, 5 games? Yeah."
The 36-year-old pivotman had posted averages of 14.9 points, 7.8 rebounds and 2.3 assists over 65 games this season before missing Saturday's contest against Memphis.
Former Titans kicker dies in car crash
UPI Sports Results for September 20, 2014