Left-hander Ron Mahay, senior member of the Royals, was designated for assignment on Monday and right-hander Yasuhiko Yabuta was called up from Triple-A Omaha to replace him.
Mahay, 38, had a 1-1 record and 4.79 ERA in 41 relief appearances this season, his second with the Royals. Last year he went 5-0 with a 3.48 ERA in 57 games.
Yabuta has spent the entire season with Omaha, going 2-1 with a 3.55 ERA in 26 games. He had 53 strikeouts in 45 2/3 innings.
Yabuta was signed out of the Japan League before the 2008 season but struggled and spent part of the summer with Omaha. He was 1-3 with a 4.78 ERA in 31 games last year for Kansas City