The Angels said after their 2-1 victory over the Twins that Middleton was removed because of right elbow discomfort. He will have an MRI on Monday, the team said.
Middleton just came off the disabled list Thursday. He was put on the DL on May 2 because of elbow inflammation.
Middleton threw only 12 pitches and recorded two outs Sunday before he was removed. He was relieved by reliever Jim Johnson.
Middleton leads the Angels with six saves.