ARLINGTON -- Sidelined with shoulder tendinitis, A's rookie right-hander Vin Mazzaro hasn't pitched in a game since Aug. 29.
He might not pitch again this year.
Oakland manager Bob Geren on Monday said that Mazzaro's most recent throwing session, Sunday in Minnesota, "didn't go as good we we'd have liked; below average."
Asked if the idea of shutting down Mazzaro has been discussed, Geren quickly nodded his head in the affirmative.
"Yes," Geren said before the scheduled opener of a three-game series against the Rangers. "It's a consideration. It's a possibility."
Mazzaro, 22, has been touted -- along with 21-year-old rookies Brett Anderson and Trevor Cahill -- as a potential frontline starter on which the A's might be able to rely for years.
He did nothing to quiet such talk when he was called up to Oakland in early June after a stellar showing at Triple-A Sacramento, dominating in his first two big league starts (two wins, zero earned runs). Since then, however, he's suffered far more downs than ups; his record is 4-9 with a 5.32 ERA.
In five July starts, Mazzaro's ERA was 8.51. In August, his only start among six that lasted longer than five innings was a 5 1/3-inning outing.
"We'll reevaluate him tomorrow and go from there," Geren said. "But as far as him [joining the rotation soon], no. That's not going to happen."
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.