Oakland, CA (SportsNetwork.com) - The Oakland Athletics optioned struggling starter Kendall Graveman to Triple-A Nashville on Sunday.

Graveman, 24, gave up six runs in 4 2/3 innings in Saturday's 9-3 loss to Houston.

The right-hander is 1-2 with an 8.27 ERA in his first four major league starts this season and has pitched beyond the fifth inning only once.

The A's filled the roster spot by recalling pitcher Ryan Cook from Nashville.

Cook, who was demoted to the minors late in spring training, didn't allow a run in 5 2/3 innings for the Sounds.