Dodgers manager Dave Roberts spoke to the media moments before the team announced the diagnosis and didn't go into specifics, saying only that Seager's hand was swollen and that he was still "in some pain" after the Dodgers' 7-0 victory at home.
Seager was hit in the back of his right hand as he went to swing at a 90 mph sinker from Detwiler. He was in noticeable pain and came out of the game shortly after being looked at by Roberts and one of the Dodgers' trainers.
Seager will be placed on the injured list Sunday, and the team is expected to call up another infielder to replace him. Earlier, the Dodgers acquired veteran infielder Yoshitomo Tsutsugo from the Tampa Bay Rays. But Roberts said Tsutsugo, who mostly plays the corner-infield spots, won't be available to join the team just yet.
Seager joins a growing list of key Dodgers players on the shelf, alongside center fielder Cody Bellinger, left fielder AJ Pollock, starting pitcher Dustin May and relief pitchers Corey Knebel, David Price and Brusdar Graterol.
Seager, a free agent at season's end, returned to prime form in 2020, batting .307/.358/.585 with 28 extra-base hits in 52 regular-season games, then winning MVP honors after each of the final two postseason rounds. His slash line was .265/.361/.422 in 169 plate appearances this season.