The Angels placed starting pitcher Garrett day disabled list Tuesday, a day after he suffered a strained right groin in the first inning of a game against Texas.
Richards, 23, was making his second career start and gave up an unearned run while recording two outs before leaving. The Angels went on to lose the game, 8-4.
The Halos made some additional moves Tuesday, optioning infielder Andrew Romine to Triple-A Salt Lake while recalling pitchers Horacio Ramirez and Trevor Bell.
The left-handed Ramirez and right-handed Bell will bolster the Angels' bullpen.
Ramirez has made five appearances for the Angels this season, allowing six runs -- five earned -- in four innings. Bell has pitched to a 3.24 ERA in 15 appearances in 2011.
Romine was recalled August 2 and was used sparingly, entering as a late-game replacement August 10 against the Yankees while starting at shortstop three days later against Toronto.