ST. LOUIS — Washington Nationals right-hander Trevor Williams said Wednesday night that an MRI exam of his elbow revealed a partial tear of the ulnar collateral ligament, and he will undergo surgery next week that will keep him out until at least next season.

Williams, who re-signed with Washington on a $14 million, two-year deal last winter, has been limited to only 30 starts over the past two seasons because of arm problems. He was 3-10 with a 6.21 ERA in 17 starts this season, his last coming July 2, when he allowed seven runs on nine hits and a walk in just three innings in a loss to Detroit.

The 33-year-old Williams only has a partial tear of the ligament, and the hope is an internal brace procedure will be enough to treat the injury. But orthopedist Jeffrey Dugas, who will perform the surgery next Thursday, said Williams could require Tommy John surgery if the ligament is more damaged than the MRI exam showed.

Interim manager Miguel Castro filled Williams’ rotation spot last weekend with Shinnosuke Ogasawara, who allowed four runs on seven hits in 2 2/3 innings in his big league debut. Ogasawara is expected to make another start this weekend in Milwaukee.