Maeda pitched 5 innings with seven strikeouts and no hits allowed in the postseason so far.
Seager's status seemed all but cemented prior to the Dodgers' workout on Monday, with manager Dave Roberts saying the 23-year-old would "aggressively take ground balls" to test the injury.
Seager, who won National League Rookie of the Year and finished third in MVP voting in 2016, hit.295/.375/.479 with 22 home runs and 33 doubles in 2017. he was 3-for-11 with a triple and three walks in the NLDS against Arizona.
Shortstop Corey Seager and right-hander Brandon McCarthy were added to the active roster for the World Series by the Los Angeles Dodgers, who dropped outfielder Curtis Granderson and backup catcher Kyle Farmer.
During the NLCS, Charlie Culberson filled in for Seager at shortstop.More news: Pats LB Dont'a Hightower out for season with torn pec
The Dodgers were hoping for a power surge out of Granderson, but he wasn't able to supply it.
McCarthy, 34, went 6-4 with a 3.98 earned-run average during the regular season. Entering the postseason the concern was on how the bullpen would perform when they couldn't finish off the regular season on good note. But the veteran was never fully healthy, whether it was a right knee injury that caused him to miss a start in July, or a recurring finger blister that caused him to miss all of August and most of September.
It's no real surprise that Granderson won't be playing against the Astros, as he was bad in spot duty for the Dodgers down the stretch, hitting.161/.288/.366 in 132 plate appearances. In three relief appearances to end the season, he allowed four runs in six innings.
The Astros did not make any changes from their roster in the American League Championship Series against the New York Yankees.