Outfielder Jarrod Dyson was recalled from Triple-A Omaha to take Cain's spot on the roster for Friday's home opener against the Cleveland Indians.
Cain was injured in the second inning Tuesday night at Oakland when he banged into the wall while making a spectacular catch that was turned into a double play. He played another inning before coming out of the game. He didn't play in Wednesday's series finale against the A's.
"Part of the problem is that this kid really uses his legs," manager Ned Yost said. "He's a speed guy, he covers a lot of ground and we want to nip this thing in the bud right now, so we don't push him seven days from now when he's not 100 percent and he re-aggravates it and it continues to affect him. So the smart thing to do is put him on the DL and let him get 100 percent [healthy] in the next two weeks."
When Cain is ready to return, Yost left open the possibility that he'd go out on a Minor League rehabilitation assignment to get some at-bats before rejoining the Royals.
Yost wasn't ready to say who would start in center field on Friday, but he'll have Dyson, Jason Bourgeois and Mitch Maier available.
"We've got some options because we've got a right-handed hitter in Bourgeois, we've got left-handed hitters in Maier and Dyson. I like Maier coming off the bench a little more, and with Dyson's ability to roam the outfield -- and he's off to a great start in Triple-A -- we'll use him a lot out there."
The Indians will start right-hander Derek Lowe on Friday afternoon.
Cain, one of the Majors' hottest hitters in Spring Training, got off to a slow start in the regular season. In five games, he's gone 2-for-15.
Dyson, one of the game's fastest players, is off to a .364 (12-for-33) start for Omaha, with six stolen bases in as many attempts.
Cain said his injury was more serious than he initially believed.
"When I hit the wall, my leg went outward and I feel like I strained it then. I felt it when I started running in, and it's something that's a little nagging now," Cain said. "My legs are a big part of my game and I've got to be sure that's right so I can get back on the field."
Cain is the sixth Kansas City player on the disabled list. Catchers Salvador Perez and Manny Pina are on the 60-day DL and pitchers Joakim Soria, Felipe Paulino and Blake Wood are on the 15-day list.
Yost said Paulino, who developed a tight forearm in Spring Training, looked good in a batting practice session before Thursday's off-day workout. Paulino is expected to head for a rehab assignment soon.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.