The Orioles placed Rasmus on the restricted list on Tuesday. Showalter told reporters that the reasons for Rasmus' decision were private.
"Colby talked to me this afternoon, and said he made a decision to go home and discontinue playing, and we're going to honor that and give him the privacy that he's due," Showalter told reporters, according to the Baltimore Sun. "I hope everything is for the best. We wish him well, and we'll see what the future brings. But I'm not going to get into a lot of details in our conversation."
Rasmus had previously retired last July when he told the Tampa Bay Rays that he was stepping away from baseball. However, he decided to return this season, signing with the Orioles in February.
He was hitting .281 with nine home runs and 23 RBIs for the Rays last season when he left the team but wasn't having as much success for the Orioles this season. He is hitting .133 with one home run and one RBI in 49 plate appearances this season.
Rasmus was sidelined for more than two months with the same hip injury that sent him to the disabled list last June with the Rays. Rasmus was activated by the Orioles on June 21.