Ohtani hit his Major League-leading 44th home run in the first inning of the opener in a doubleheader with the Cincinnati Reds but left the mound during the second inning with what the Angels said at the time was "arm fatigue".
The Japanese star had skipped his last scheduled start due to arm fatigue and was pitching for the first time since August 9th.
However, Minasian later said Ohtani had a torn ulnar collateral ligament (UCL), adding that it was too soon to tell whether surgery was required.
"We're in the process of getting second opinions," Minasian said.
"Once the information is there, he'll make the right decision on what he wants to do, and we'll support him, whatever he decides."
The Angels will take on the New York Mets on Friday and Minasian said he hoped Ohtani would be able to return as a batter this season.
"I wouldn't be surprised if he's in New York and he's in the lineup. I know how bad he wants to play," he added.
The Angels lost both games against the Reds, 9-4 and 7-3.
