A's outfielder Craig Gentry was held out of Friday's workout and underwent an MRI for a sore back.
Gentry, acquired from Texas this winter and expected to play significantly as the fourth outfielder, said he aggravated his back swinging the bat Thursday, but that it had bothered him a bit previously.
He's unsure of when he'll return to the field.
"I'm just going to keep getting treatment," Gentry said. "It's early, there's a lot of time left."
The A's have yet to receive results of the MRI.