The Oakland Athletics could be without Brett Anderson for up to six weeks after he was diagnosed with a stress fracture in his right foot.

Anderson felt pain in his foot while running in the outfield this week.

The left-hander, who came back from Tommy John surgery last summer after missing 14 months, has been on the disabled list since May 1 with a sprained right ankle.

"It's pretty frustrating, disappointing and all the other similar adjectives," Anderson said. "I was two days away from making another rehab start and now I'm in a walking boot with a fracture in my foot."