Rasmus was in camp Wednesday to finish up his physical. He received an invitation to big league spring training.
The 31-year-old Rasmus was with Tampa Bay in mid-July when the Rays said he was going to step away from baseball. Neither the team nor Rasmus offered an explanation, though he had been slowed by hip trouble.
Rasmus was hitting .281 with nine home runs and 23 RBIs in 37 games for the Rays when he left. He has hit 165 home runs and batted .242 in nine seasons with St. Louis, Toronto, Houston and Tampa Bay. He has hit more than 20 home runs in a season four times in his career.
The left-handed-hitting Rasmus is expected to compete with Alex Presley, another left-handed-hitting outfielder, for a spot on the major league roster.
Orioles general manager Dan Duquette said in a text that "Rasmus is a proven veteran player in the AL East, who is a versatile outfielder with good power and speed to make a meaningful contribution."