The right-hander received a second opinion on the damaged ulnar collateral ligament from Los Angeles Dodgers head team physician Dr. Neal ElAttrache.
"While this is unfortunate, we have no doubt that Noah will be able to return to full strength and continue to be an integral part of our championship pursuits in the future,” said Van Wagenen, Syndergaard's former agent.
Nicknamed Thor, Syndergaard was the No. 2 starter in a strong rotation behind two-time NL Cy Young Award winner Jacob deGrom. New York has for now sufficient starters to make up for Syndergaard's absence, with Marcus Stroman, Michael Wacha, Rick Porcello and Steven Matz.
Syndergaard turns 28 in August and currently is eligible to become a free agent after the 2021 season. He agreed in January to a $9.7 million, one-year contract.
Syndergaard was an All-Star in 2016 when he went 14-9 with a 2.60 ERA but his ERA has climbed to 2.97 in 2017, 3.05 in 2018 and 4.28 last year, when he was 10-8 in 32 starts.
He pitched eight innings over three spring training starts, allowing four runs — three earned — and five hits with 11 strikeouts and no walks.