Lucas Giolito (27) with the Guardians in 2023. David Richard-USA TODAY Sports

Red Sox right-hander Lucas Giolito experienced discomfort in his right elbow after his most recent throwing session, manager Alex Cora announced Tuesday, per Jen McCaffrey of The Athletic. He’ll undergo additional testing, but ESPN’s Jeff Passan reports that the initial diagnosis is a partial tear of the right ulnar collateral ligament (UCL) and a flexor strain. A determination on treatment won’t be made until Giolito receives additional opinions, but season-ending surgery is now on the table.

It’s a brutal blow for the Red Sox, who signed Giolito to a two-year, $38.5M contract that allows the right-hander to opt out following the 2024 campaign. Assuming additional opinions confirm the team’s initial diagnosis, Giolito’s decision on next year’s $19M player option will be rendered a foregone conclusion before the season begins. If he picks up that player option, the team would be granted a $14M club option for the 2026 season. Giolito could then convert that into a mutual option by pitching 140 innings in 2025.

Giolito, 29, signed his current deal in hopes of putting a rough couple of years behind him and reentering the market in a stronger position. From 2022-23, the right-hander logged 346 innings but pitched to an ineffective 4.89 ERA between the White Sox, Angels and Guardians. A spike in Giolito’s home run rate contributed heavily to the downturn in performance. Still, he maintained a better-than-average 25.5% strikeout rate against a slightly higher-than-average 9% walk rate in that span.

The primary culprit in Giolito’s struggles was a spike in home run rate; metrics like xFIP (4.08) and SIERA (4.01) felt he was better over the past two seasons than his earned run average would indicate — but also still worse than he was in 2019-21 peak when he fanned nearly 31% of his opponents against a stronger 8% walk rate.

With Giolito’s entire season in doubt, any chances of rebounding could well be placed on hold for a year or more. At the very least, he’s in for a lengthy IL stint and will be absent to begin the season. That leaves Brayan Bello, Nick Pivetta, Tanner Houck, Kutter Crawford and Garrett Whitlock as the likeliest options to open the season in Boston’s rotation. Others on the 40-man roster include Brandon Walter, Chris Murphy and Cooper Criswell. The Sox have not yet added much in the way of veteran arms on non-roster deals to compete for jobs this spring, and they traded lefty Chris Sale to the Braves in the swap that brought second baseman Vaughn Grissom back to Boston.

A major injury to Giolito will undoubtedly fuel speculation regarding the top remaining arms on the market. Red Sox fans have clamored for Jordan Montgomery for much of the offseason. The team has spoken to him and shown interest at multiple points, including just before spring training. Montgomery's Boston connection is particularly strong, as his wife is doing her medical residency in the city. Ownership and/or the front office have resisted meeting the 31-year-old’s asking price, but the pressure to make some move will only increase.

While fellow Boras Corporation clients Cody Bellinger, Matt Chapman and (reportedly) Blake Snell shifted from seeking long-term deals to opt-out-laden short-term deals, all indications regarding Montgomery have been that he’s still seeking a long-term deal. The Red Sox will need to weigh that while determining whether they want to throw more resources at a team that appears poorly positioned to contend for a postseason spot.

Montgomery wouldn’t cost the Sox a draft pick or international money, as he didn’t receive a qualifying offer, and the Sox are about $35M from the luxury tax threshold so that Montgomery wouldn’t push them to that point either. Snell rejected a QO, which would thus cost the Sox their second-best draft pick and $1M of space in next year’s bonus pool for international amateur free agency. There are, of course, alternative options who’ve also not yet signed. For instance, Michael Lorenzen and Mike Clevinger are both still available and performed reasonably well in the majors just last season.

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