The Royals were already reeling from the injuries suffered by starting catcher Salvador Perez (left knee surgery) and closer Joakim Soria (right elbow ligament damage).
"I was scared, too, because it really hurt. It was really a hard ground ball," Mendoza said. "The trainers said we're going to wait until [Thursday] morning to see what's going on. Right now, I'm glad it's nothing serious."
Mendoza worked out of a first-inning jam, stranding Jemile Weeks and Daric Barton, who opened the game with singles. After Allen's single to start the second, the A's loaded the bases against left-hander Francisley Bueno, but he also escaped without a run scoring.
In 11 2/3 Cactus League innings, Mendoza has given up just one run for a 0.77 ERA and has 12 strikeouts against one walk. Despite his short outing, under Spring Training rules he got the victory and stands 4-0 in four starts. He's competing for a spot in the starting rotation with Felipe Paulino, Danny Duffy and Everett Teaford.
"He's been really good. He's commanded the ball really well. He's had real good movement on his two-seamer, he moves the ball in and he moves the ball out," Yost said of Mendoza.
Yost, however, would not commit to putting Mendoza among his five starters.
"We still have time, but he's definitely in the mix," the skipper said.
The decision to remove Mendoza from the game was primarily precautionary.
"It hit him pretty good and it's not something you want to continue with at this point of the year," Yost said. "You don't want a chance of it swelling or him altering his mechanics at all because he's throwing the ball so well. We just take him out, and put ice on it and go to work. He's fine."