Rios has been sidelined since April 13, when he was he by a pitch from Minnesota's J.R. Graham. He joined the Royals on Friday after a four-game injury rehabilitation assignment with Triple-A Omaha.
He started the season 9 for 29 (.321) with one homer and eight RBIs.
''He was really swinging the bat good when he left,'' manager Ned Yost said. ''But it may take him some time.''
Rios agreed during the offseason to an $11 million, one-year contract.
''I'm ready to do stuff out there like normal,'' Rios said. ''Everything went well. I was able to swing the bat with no issues.''