Middleton had a second opinion on the elbow after he went back on the 10-day disabled list Monday.
A date for surgery and timeline thereafter has not been announced. Middleton lasted just 12 pitches in the eighth inning of the Angels’ 2-1 win over Minnesota on Sunday, abruptly leaving with a 1-1 count on Eddie Rosario.
He had appeared in three games in four days after initially returning from the disabled list with elbow inflammation.
Middleton was the Angels’ closer in April, getting six saves. He has a 2.04 ERA in 16 appearances this season, his second in the majors.
The Associated Press contributed to this report.