OAKLAND -- One of the better stories of the A's season, albeit a short story, came to an end on Monday when right-hander Brett Tomko was declared finished for the season.

Tomko, signed to a Minor League deal after being released by the Yankees in early August, went 4-1 with a 2.95 ERA in six starts with Oakland but hasn't pitched since earning his 100th career victory with a five-hit shutout against the host Rangers on Aug. 14.

A free agent this winter, Tomko, 37, told MLB.com on Tuesday that an MRI done that morning had revealed a pinched nerve in his right shoulder, causing discomfort and numbness throughout his arm.

"Tomko will not pitch again this season, that's for sure," A's manager Bob Geren said Monday before the opener of a three-game series against Texas at Oakland-Alameda County Coliseum.

The A's haven't gone through the formality of putting Tomko on the 60-day disabled list, suggesting that Oakland has no plans to add any players not on the 40-man roster to the big league club for the season's final 12 games.