Royals manager Ned Yost said after the game that Cain's injury was definitely a hamstring strain.
"He'll see [Dr. Vincent Key] tomorrow and we'll know more then," Yost said.
Asked if Cain would get an MRI, Yost said, "We'll have an MRI sometime, as soon as we can get him in."
But Yost said he had no indication how severe the strain might be.
"You guys want to know what I don't know," Yost said. "Nobody knows. Doc will look at him tomorrow. I wish I had an answer but I don't."
Cain did not speak to reporters after the game. He showered, dressed and walked on his own to the training room with trainer Nick Kenney. Not surprisingly, Cain wore a look of frustration.
Cain's injury is just one of several that have hit the Royals this season. Third baseman Mike Moustakas is out for the season after ACL surgery. Alex Gordon missed a month with a broken bone near his right wrist. Catcher Salvador Perez missed time because of a quad contusion.
Starter Chris Young was on the disabled list with a strained forearm before returning, and starter Kris Medlen is on the disabled list with a rotator cuff strain.
But Gordon said there has to be a next man up mentality on this team.
"We don't know what's wrong with Cain yet," Gordon said. "We're hoping the best. If he goes down, we got a guy that can step in with Dyson. Obviously, Cain is one of a kind. We've seen [Dyson] step in before and do the job. Hopefully [the injury] is nothing."
Cain has been able to avoid the disabled list since April of 2014, when a left groin strain put him on the shelf. He had the same injury in '12 that required a DL stint. In '13, a pulled oblique put him on the disabled list.
If Cain requires another trip to the DL, the Royals do have rookie outfielder Brett Eibner, who had success in two brief stints with the Royals this season, available at Triple-A. But Eibner is a corner outfielder, and thus Dyson and Paulo Orlando are the likely options in center, if needed.