Rasmus, 30, hit .206/.286/.355 with 15 home runs in 107 games last season with the Astros. It was his fifth straight season with 15-plus homers, joining Mike Trout, Adam Jones and Jose Bautista as the only American League outfielders with such a streak.
Rasmus is a .241/.311/.434 career hitter in eight seasons with the Cardinals, Blue Jays and Astros.
Outfielder Jason Coats was designated for assignment to make room for Rasmus on the 40-man roster. Coats, 26, was claimed off waivers from the White Sox on Jan. 11.
Cash Kruth is a reporter for MLB.