NEW YORK -- Mets top pitching prospect Matt Allan, the linchpin of an aggressive 2019 Draft strategy and the No. 3 prospect in the organization per MLB Pipeline (No. 64 overall), will undergo Tommy John surgery to repair a partial tear of his ulnar collateral ligament, the team announced Friday. Allan will miss the entire 2021 season and likely a chunk of next year as well.

The Mets selected Allan in the third round of the 2019 Draft despite signability concerns at the time. Widely considered a first-round talent, Allan wound up signing for $2.5 million -- or around $1.9 million over his slot value. The Mets made up the difference by drafting exclusively college seniors with the rest of their Top 10 picks, essentially gearing their entire Draft strategy around pooling together enough money to sign Allan.

This spring, the Mets paired Allan with Jacob deGrom during drills and bullpen sessions, hoping he could soak up wisdom from the two-time Cy Young Award winner. Allan put together an impressive camp, reaching the upper-90s with his fastball, and was assigned to High-A Brooklyn for the start of what was to be his first full professional season. Instead, before making a single appearance, Allan underwent an MRI this week that revealed the ligament tear.

Mets medical director Dr. David Altchek confirmed the diagnosis of a partial tear and the recommendation of Tommy John surgery. The operation typically requires a recovery period of 12-18 months; given that Allan is a prospect, the Mets are likely to tread carefully with him and lean toward the longer end of that timeframe. General manager Zack Scott was out of town on Friday and unable to comment on Allan’s status, according to a Mets spokesman.

Although surgeries are never happy news for pitchers, Tommy John operations remain common, with good long-term prognoses. Current Mets deGrom, Noah Syndergaard and Taijuan Walker have all undergone the operation, as have prospects J.T. Ginn, Thomas Szapucki and Franklyn Kilome. Former Mets Zack Wheeler, Matt Harvey and Steven Matz also recovered from Tommy John surgeries while with the organization.

“His poise, his maturity has been impressive,” Mets manager Luis Rojas said of Allan in February. “He definitely behaves like an older person.”

Upon signing in 2019, Allan produced a 1.08 ERA over five outings in his professional debut for the Gulf Coast Mets, before earning a promotion to Brooklyn for the New York-Penn League playoffs. Allan pitched three scoreless innings in the Cyclones’ championship clincher, hinting at what the Mets still hope will be a successful career to come.

“I want to do that again, wherever I’m at,” Allan said during Spring Training. “I want to be part of a championship team.”