ST. LOUIS – Trevor Williams has a partial tear of his elbow ligament, one that will require a surgical procedure that will sideline the Nationals' right-hander until at least early next season, possibly most of the season.

An MRI taken of Williams’ elbow revealed a partial tear of the ulnar collateral ligament. Because it’s not a full tear, doctors believe it can be treated with an internal brace procedure, the relatively recent, less-invasive surgery that allows a pitcher to return in approximately nine months. Williams will be operated on next Thursday by Alabama orthopedist Jeffrey Dugas, who did caution the 33-year-old he might actually need to perform Tommy John surgery if the ligament appears to be more damaged once he sees it firsthand.

If the internal brace procedure is all that’s required, Williams was told he could return to pitch next April or May. If the ligament has to be reconstructed via Tommy John surgery, he would miss most – potentially all – of the 2026 season.

“It’s unfortunate that’s what it is,” he said. “But I’m glad that we’re going to be able to fix it and get it right.”

The news comes as a blow both to Williams, who made only 30 combined starts the last two seasons due to arm issues, and to the Nationals, who re-signed him to a two-year, $14 million contract over the winter.

Williams spent 3 1/2 months rehabbing a lesser forearm injury, returning in time to make two September starts that left him with solid season stats: 6-1 with a 2.03 ERA and 1.035 WHIP over 66 2/3 innings. Former general manager Mike Rizzo then re-signed the veteran to a two-year deal in December, only to watch as he struggled to a 3-10 record, 6.21 ERA and 1.536 WHIP before landing on the injured list last week after complaining of elbow soreness.

Though he was disappointed to learn the news in recent days, Williams was relieved when he heard he may not have to miss an entire calendar year, thanks to the same procedure a number of big leaguers (including now-Nationals pitching strategist Sean Doolittle) have undergone in recent years as an alternative to Tommy John surgery, in which doctors typically remove a tendon from the hamstring and insert it into the elbow to replace the torn ligament.

“It’s a miracle surgery, for what it is,” he said. “I’m hoping to wake up on Thursday and have my hamstring not hurt. Because that would mean it was just the brace. It stinks, it’s unfortunate. But I’m looking forward to getting it as strong as possible and cleaning up some things I need to clean up with my delivery and my mechanics to get me to the point where I need to be.”

The Nats filled Williams’ rotation spot last weekend with Shinnosuke Ogasawara, the 27-year-old Japanese left-hander who was roughed up for four runs and seven hits in only 2 2/3 innings in his major league debut. Interim manager Miguel Cairo said the plan is for Ogasawara to make another start this weekend in Milwaukee, after which the club will evaluate the situation.

“As of right now, he’s going to be in that spot,” Cairo said. “I will let you guys know if that’s going to change. But right now, it’s him.”

Top pitching prospect Cade Cavalli appeared to be on the verge of a promotion, but the 2020 first round pick has given up seven runs in each of his last two starts for Triple-A Rochester, putting on hold for now any thoughts of a call-up.

* Keibert Ruiz’s re-placement on the 7-day concussion IL has club officials concerned about the catcher’s health in both the short- and long-term.

Ruiz went back on the IL on Tuesday, three days after he took a foul ball off his mask in his most recent game appearance. That incident came only one day after he was activated from his first stint on the IL, the result of a concussion he suffered June 23 when he was struck in the head by a foul ball while watching from the dugout railing in San Diego.

Ruiz had passed all tests required by Major League Baseball to return last week, but the fact he took another blow to the head so soon afterward is cause for concern.

“It’s very delicate, when it’s the head,” Cairo said. “We’ve got to be thinking about his health first. Right now, hopefully he recovers. We’re going to make sure he’s 100 percent before he comes back.”

* An MRI taken of Derek Law’s elbow showed no structural damage, a relief for the veteran right-hander who continues to try to get himself healthy enough to make his long-awaited season debut.

Law has twice been shut down in recent weeks after experiencing elbow discomfort the day after he pitched for Rochester. He’ll give it another go soon and hope to avoid the same issues this time around, confident now at least he isn’t dealing with a major injury.

“That was good news to hear,” Cairo said. “It was refreshing to hear that everything is fine.”