Another left-hander, John Bale, ended his injury rehabilitation assignment and is headed back to Arizona.
Meanwhile, outfielder David DeJesus returned to the lineup after missing five games because of a sore back. He was in center field and batting third against the Twins on Friday night.
"It's good to have his bat back in there," manager Trey Hillman said. "And leaving Mike [Aviles] in the leadoff spot just seemed to be the natural thing to do because he's been so successful, and it doesn't seem to affect David no matter where we hit him in the top three spots."
Aviles batted leadoff while DeJesus was out, and went 9-for-21 (.429) in the five games. DeJesus has batted first in 82 games, but Hillman had placed him No. 3 in seven previous games.
Outfielder Joey Gathright -- a leadoff batter on 20 occasions this season -- is on the disabled list with a right shoulder injury, and was to begin his rehab assignment with Triple-A Omaha on Friday night.
Mahay is suffering from plantar fasciitis, which is heel pain caused by inflammation of tissue supporting the arch of the foot. In Mahay's case, the pain affects his pushoff foot as he delivers a pitch.
"It's been bothering him for a while," Hillman said. "He just hasn't said anything."
Mahay, one of the Royals' top relievers this season with a 2.62 ERA, has been roughed up in two of his past three outings.
Bale started the season in the Royals' rotation, but has been on the disabled list since April 17 -- first with left shoulder fatigue and then with a left hand fracture.
He pitched for Omaha in his recent rehab assignment, appearing in seven games with a 0-2 record and an 8.22 ERA. He also pitched twice for Double-A Northwest Arkansas.
Bale said his hand is OK, and an MRI of his shoulder showed a "stress reaction" -- which he said is similar to a stone bruise. He had a cortisone shot, and the lefty is heading for the Royals' complex at Surprise, Ariz., to resume throwing in about three days.
"I'd like to be back in September and help the team out," Bale said.
His primary problem has been regaining velocity on his fastball, which he said was around 88 mph.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.