The Twins made the moves on Thursday after both players struggled in a 7-2 loss to the Kansas City Royals. Diamond (5-10) gave up seven runs — six earned — on nine hits in five innings. He has failed to pitch at least six innings in four of his last five starts.
A native of Guelph, Ont., Diamond was signed by the Atlanta Braves as an amateur free agent in 2007. He made his MLB debut with the Twins in 2011.
The 27-year-old was 12-9 with a 3.54 earned-run average through 27 starts with the Twins last season. He underwent surgery in December to remove bone chips from his throwing elbow.
Hicks went 0 for 4 with two strikeouts to drop his batting average to .192. Since the All-Star break, he is hitting .162 (7 for 43).
The Twins recalled outfielder Oswaldo Arcia to take one of the roster spots. Twins manager Ron Gardenhire says they will wait until Saturday to make a pitching move.