Hayes was 3-for-11 with the Royals when he was first up, and at Omaha hit .233 with 17 homers and 44 RBIs.
"We have had some problems with Salvador getting some balls [hit] off his head -- he had the concussion -- and Kottaras has also taken some balls off his head," said manager Ned Yost. "It's important to have some protection up here for both of those guys."
Bueno, meanwhile, has made one Major League appearance this season, picking up a win after throwing 2 1/3 innings of relief against the Red Sox earlier this month.
In 36 games with the Storm Chasers, Bueno was 3-3 with a 2.66 ERA. He struck out 56 batters, while walking 24 over 67 2/3 innings.
"He's another left-hander we can match up with lefties," said Yost. "He gives us other matchup opportunities."
Chris Toman is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.