Triple-A Las Vegas placed Klein on its 7-day injured list Aug. 31 with an unspecified injury.
Klein was optioned to Triple-A Las Vegas on Saturday.
The Athletics acquired Klein from the Royals on Tuesday in the Lucas Erceg trade, Mark Feinsand of MLB.com reports.
The Royals recalled Klein from Triple-A Omaha on Monday.
The Royals optioned Klein to Triple-A Omaha on Monday.
Kansas City recalled Klein from Triple-A Omaha on Friday.
The Royals optioned Klein to Triple-A Omaha on Monday.
The Royals recalled Klein from Triple-A Omaha on Thursday.
The Royals optioned Klein to Triple-A Omaha on Friday.
The Royals selected Klein to their 40-man roster Tuesday.