Severino missed almost all of last season due to lat and shoulder issues. After making three regular season appearances and two postseason appearances - pitching a combined 20.1 innings in all - the expectation was that he'd get a full, regular offseason's worth of rest and come back for 2020. Almost as soon as spring training began, however, he was shut down due to forearm soreness. It later came out that he had been experiencing that soreness since last year's ALCS. He has spent the last several days in New York consulting with physicians.
Severino went 19-8 in 32 starts in 2018, posting a 3.39 ERA across 191.1 innings, after which he signed a four-year, $40 million contract extension. At the time it was derided by many as below-market, but given the risk posed to his career at this point, it looks like a fortunate safety net for the hurler. As it is, assuming he goes under the knife, he will have basically missed two seasons and, in all likelihood, a little bit of change before he pitches again.
As for the Yankees, they entered spring training believing that they'd have a rotation of Gerrit Cole, James Paxton, Masahrio Tanaka, Severino, and J.A. Happ, with the return of Domingo Germán once he returns from suspension. Now that Severino is out - and given that Paxton is out for 3-4 months due to back surgery as well - it's Cole, Tanaka, Happ, Jordan Montgomery and . . . field.
Given the Yankees' firepower they should still be OK, but their battle to fend off the Rays just got that much harder.
The big question Brian Cashman and everyone in the Yankees needs to answer now is why a dye contrast MRI was not done before now given that Severino had been feeling discomfort since last fall. If this had been caught then, he could've at least had a mostly normal 2020-21 offseason and been ready for next year. As it is now, he likely won't have a full 2021, even if everything goes right with surgery and rehab.