It's just weakness at this point, not pain, and he was at least able to get through 18 pitches Sunday. Still, it's a worry for the Tigers, who have been trying to figure out Villarreal's on-again, off-again control and will now have his elbow checked out.
"You've got to find out the health issue. That's No. 1," manager Jim Leyland said. "Eventually you find out if he's OK. I don't know. He's not throwing good right now.
"He's gotten out of kilter right now for some reason. I don't have the answer to what that reason is, but you have to be able to do that up here. You have to be able to come back the next day and pitch because you're not going to use the other guys behind three runs. That's why we needed an inning from him."
Villarreal said he first felt some weakness after the All-Star break, when he was sidelined for the series in Baltimore. It went away, but apparently resurfaced in recent days.
"I felt like it was inflammation," Villarreal said. "It was weak, but I'm not sure what I've got. They're going to check me tomorrow."
That examination will take place in Minneapolis, where the Tigers have three games coming up against the Twins.
Villarreal took the loss against the Rangers on Saturday night after walking his first two batters in the ninth inning of a tie game. Leyland brought him back Sunday in an effort to get him past that but watched him give up two runs on as many hits with two wild pitches, all while retiring only one batter.