"He's not going to pitch the rest of the season," manager Bob Melvin said. "It's a Grade 2 strain. Unfortunately, that's the case."
As of Thursday morning, the A's had been waiting for the results of an MRI exam on the strained oblique he suffered in Wednesday's game. At the time, Melvin went as far as saying the lefty Anderson would be unlikely to make his next start.
But the results of the MRI revealed it would be more.
"It's an unfortunate situation," Anderson said. "But this team has handled adversity all year and have been able to overcome it and played well. Hopefully we can continue to do it. Guys have been contributing tremendously with guys being gone."
Anderson was 4-2 with a 2.57 ERA in six starts this season, as he had seemingly regained old form after recovering from Tommy John surgery. And prior to Wednesday's injury-shortened outing, he was 4-1 with a 1.93 ERA.
"I was throwing the ball well, feeling good," he said. "It was a fluke deal where that kind of happens and you don't really suspect it at all, and next thing you know, you're out of it. It's kind of disheartening from that aspect, but from the team aspect, these guys have been picking each other up all season."
While he'll miss the final games of the regular season, Melvin didn't rule him out for the postseason.
"If it went that far, we'd take a look at that, but we're just concentrating on the regular season now, and he will not be available during that period."
Anderson wouldn't rule it out either.
"They didn't really say. They just said do the rehab and see where you're at," he said. "Usually it takes a week or so to come back and feel good and then go from there. ... I've never been to the postseason, so I'm going to do all I can to get there.
"I would be a good story if I could come back and play in the play-in game, but we'll see how it goes."