OAKLAND -- The A's on Thursday optioned one of their promising young starters to Triple-A Nashville.

Right-hander Jharel Cotton, who has struggled to produce consistent results this season, was sent to the Minors on the club's off-day. His departure clears room for lefty Sean Manaea, who is expected to come off the disabled list next week after missing two starts with a shoulder strain.

The A's did not immediately make a corresponding move, though it's expected that catcher Josh Phegley, currently on the seven-day concussion DL, will be activated and take his roster spot Friday in Texas.

Cotton, who opened the season in the third spot of the rotation, pitched well at times, but also gave up at least five runs in three of his seven outings, yielding a 3-4 record and 5.68 ERA.

Most recently, the right-hander took a loss against the Angels on Tuesday after allowing seven runs on eight hits, including three home runs.

Cotton's 35 strikeouts lead Major League rookies, and his 38 innings pitched are tops among American League rookies, but command often escaped the young pitcher, an issue he'll be allowed to harness at the Minor League level.

Cotton, 25, came to the A's in last year's deal with the Dodgers that sent Josh Reddick and Rich Hill to Los Angeles.