The 28-year-old ace said afterward that he wasn't concerned about the issue, but he underwent a precautionary MRI Friday, which revealed the strain.
"Oddly enough, I feel pretty much 100 percent normal right now," Richards said Friday before the Angels' home opener against the Mariners. "There is obviously a strain, so the smart thing to do would be to kind of let it calm down. It's kind of what we're doing right now, but I feel totally fine, with the exception of that. My elbow is in great shape, and they've already looked over my shoulder and everything. It's the best that we could have hoped for at this point."
Richards said he will refrain from throwing for five to seven days and is aiming to pick up a baseball again Tuesday. After that, he would have to throw a bullpen session before sliding back into the rotation. He is slated to miss his next scheduled start against the Rangers on Tuesday, but he is eligible to be activated off the disabled list on April 16, meaning he could miss only one turn in the rotation if he recovers as expected.
"The information from our medical department is encouraging to the extent that it's relatively minor," manager Mike Scioscia said. "We're hoping just keeping him away from throwing a baseball for about a week will get this behind him, and then we'll just see how he responds to his bullpens and when he's ready to go. But considering where Garrett was last year, this is just a little minor bump in the road."
Richards missed almost the entire 2016 season after being diagnosed with a partially torn ulnar collateral ligament in his right elbow, though he avoided Tommy John surgery by undergoing stem-cell therapy.
Scioscia originally said Wednesday that the Angels had no plans for Richards to undergo an MRI and were hopeful that he would make his next start. But the club reversed course Thursday and decided to run the test as a precautionary measure.
"I think it's just a precautionary thing," Richards said. "Missing one start now might prolong the season. It might be even beneficial for me moving forward, instead of just rushing me back."
Scioscia said the Angels were weighing whether to have another pitcher make a spot start Tuesday or just use Monday's off-day to skip Richards' turn in the rotation. If they opt for the latter, left-hander Tyler Skaggs would start against the Rangers Tuesday on normal rest. Two of the Angels' options to take Richards' spot in the rotation would be reliever Yusmeiro Petit, who is currently stretched out in the bullpen, or Alex Meyer, who is in Triple-A Salt Lake.
"We're going to get through this weekend first, and we're going to look at all the options we have and what makes best sense for our whole staff," Scioscia said.
Mike Morin was recalled from Triple-A Salt Lake to take Richards' spot on the roster.