Relievers Mike Morin and Cam Bedrosian, and shortstop Ryan Jackson were called up from Triple-A to take their place on the roster.
Featherston was placed on the DL with what the team called an upper back strain; Rasmus has a right forearm strain.
The Angels nonetheless needed fresh bullpen arms, after Shoemaker gave up six runs in the second inning on Saturday. With Shoemaker down, the Angels have only four starters. They'll need a fifth against the White Sox on Thursday, but Nick Tropeano -- currently slated to start on Wednesday -- can be pushed back to make that start.