"Each pitch I would get to my power position to throw, and I would turn and it would feel like somebody was jabbing me there," Anderson said. "It's kind of one of those fluke deals where it wasn't one pitch or one play. I thought it was a cramp, and obviously it was worse than that. It's sore to the touch and sore when I do certain movements and stuff, and it kind of bothers me to sit."
Oblique injuries typically call for at least two weeks of rest and often more, meaning Anderson likely isn't to be ready until postseason play, should the A's participate.
"I don't think it's anything real serious, but obviously they're going to take the most precautions with him, being as how good he is," catcher Derek Norris said. "You don't want to risk something that could take him out a long period of time. Hopefully he'll bounce back quick."
"It definitely hurts, but hopefully just like the rest of the year's gone, someone will step in his shoes and do a good job for us."
With one out in the third inning, Anderson fell to the ground while throwing a 2-2 pitch -- his 48th of the night -- to Delmon Young, departing the game with the bases loaded having already given up two runs in the frame. He finished allowing three runs on three hits and three walks in 2 1/3 innings, with one strikeout.
"Coming into the inning, he was a little bit tight, and we could see a couple pitches he was stretching his back," manager Bob Melvin said. "We just didn't want to go any farther with it."
"He tweaked his oblique a few pitches before, threw a few more and said it just didn't feel right," Norris said. "With the cold weather, it tightened up on him and he couldn't loosen up."
Righty Pat Neshek was called in from the bullpen to replace Anderson, who was making his sixth start of a season that was previously defined by Tommy John rehab. Before a five-run outing against the Angels last week, Anderson had surrendered just two combined runs over his first 26 innings.
"It's pretty disheartening [after] the way I've been throwing," Anderson said. "To come back after surgery and six starts into it, have some other kind of fluke injury that I don't really know how it happened. It wasn't like a one-pitch deal. It was over the course of 10 minutes."
Should Anderson miss his next start Monday in Texas, as he's expected to, the A's are set to start rookie Dan Straily against the Rangers. Straily was originally scheduled to go Saturday in New York, but Melvin has decided to go with lefty Travis Blackley instead.
Oakland just began a crucial 10-game road trip through Detroit, New York and Texas and, outside of Anderson and Blackley, its other four starters on the roster are all rookies.
"He's done amazing for us," Blackley said of Anderson. "It's not someone you can just replace. Everyone's going to need to pick up the slack and just try to do what we can to keep the ship moving. He'll definitely be missed. We've had some rough ones, obviously with [McCarthy] and [Colon], but it seems like guys have stepped up and done the job in their stead. We're still confident as a team. Not too much is going to overwhelm us."