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 past five starts.
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.