Manager Scott Servais said Seager will have surgery Tuesday to repair the tendon of his middle finger. Seager had an MRI over the weekend that revealed the extent of the injury, which is just above the knuckle.
This will be Seager's first time on the injured list. It's unclear how long he will be out.
Seager is coming off the worst season of his career in 2018, when he hit .221. He changed his offseason training regimen and arrived at spring training slimmed down and in better condition. He was hitting .318 in nine spring training games.
With Seager out, the Mariners are likely to move Ryon Healy to third base. Healy played in only two games at third base last season with Seattle, but made 103 starts at third during the 2016 and 2017 seasons with Oakland.