Anderson was pulled from Saturday's contest having allowed just one run and three hits through six solid innings against Cleveland after experiencing the same type of soreness that flared up during Spring Training last year.
As a precaution, Geren said that the left-hander won't try to throw again until Tuesday, when the club is scheduled to play its first of two games at Tampa Bay.
"It's one of those things where we really won't know much until he throws again," the A's skipper said. "It's not something that affects him when he's doing everyday things, so he'll receive treatment and we'll go from there."
The 22-year-old Anderson, who just last week signed a new contract worth up to $31 million, is hopeful he'll make his next start Friday in Toronto, but Geren mentioned the club's off-day Monday provides flexibility in the event he can't take the mound.