The Los Angeles Angels of Anaheim optioned A Salt Lake on Thursday.
Chatwood has seen his earned-run average rise from 3.64 to 4.35 over his last four starts, most recently surrendering five runs in two-plus innings against Texas on Tuesday.
In 23 starts this season, the 21-year-old righty has posted a 6-9 record with a 1.60 walks/hits per innings pitched.
To fill his spot on the roster, the club recalled catcher Hank Conger from its Triple-A affiliate. Conger was sent down to the minors in mid-July after hitting just .214 with five homers and 16 RBI in 50 games with the big club.