The Angels also recalled right-hander Eduardo Paredes from Triple-A Salt Lake on Tuesday.
The hard-throwing reliever emerged as the Angels' presumptive closer last month with a strong start to his second big league season. He converted six of seven save opportunities with a 2.40 ERA in 13 appearances.
He felt pain in his elbow last weekend, but Middleton says his elbow already feels better with two days of rest. The DL move was retroactive to Saturday and Middleton expects to return to the active roster as soon as he is eligible for reinstatement on May 8.
The Angels had lost four straight heading into their series opener against Baltimore on Tuesday night.