That could be iffy, though, because the Cactus League opener is on Friday afternoon against the Rangers.
"It's very minor, not anything that we're looking to be a hampering, recurring type of thing," manager Ned Yost said.
Cain initially strained the hand a few days ago and it's continued to bother him.
"He did it while he was in the cage, by himself, doing one-hand drills, which he probably shouldn't have been doing," Yost said.
The injury to Cain is drawing considerable attention because he proved injury-prone last season, missing all but 61 games due to three leg ailments. There's always the possibility that Cain's status as the starting center fielder could become vulnerable.
"We'll see," Yost said. "[Jarrod] Dyson's there, knocking on the door, too. We've got depth there. You've got to be healthy to play."
The Royals also have David Lough on the 40-man roster and three other possible center fielders: Endy Chavez, Luis Durango and Willy Taveras were signed as Minor League free agents and are in the Major League camp.