To replace Cain, the Royals recalled Jason Bourgeois from Triple-A Omaha. He started in center field and was the leadoff hitter on Friday -- going 2-for-3 with two stolen bases and a run scored in the series opener.
Yost indicated that Bourgeois, a right-handed batter, and left-handed David Lough could be used in a platoon situation as the season winds down.
Bourgeois, 30, spent most of the season in a part-time role with Omaha, batting .243 in 60 games for the Storm Chasers. He also had two stints with Kansas City, batting .333 (11-for-33) in 19 games. Omaha is currently involved in the Pacific Coast League championship series.
Cain was injured while chasing a double hit by the Twins' Alexi Casilla in the 10th inning of the Royals' 4-3 loss on Thursday night at Minnesota.
"When I was running, probably the step before the dive, I felt something," Cain said. "Once I loaded up and made the dive, I felt my whole leg just kind of grab. I was in a lot of pain. It's just something I have to deal with. Injuries have found a way to find me this year. It's been crazy."
It's the latest injury to the speedster's legs.
In the fifth game of the season at Oakland, Cain sustained a left groin strain when banging into the wall making a catch. While recuperating from that on a Minor League rehabilitation assignment, he incurred a torn left hip flexor. He missed 78 games before returning on July 13.
Now it's his right leg that is under treatment.
Cain was playing well with his left leg apparently back to full strength. He hit safely in his last eight games (.378, 14-for-37) with six RBIs, six extra-base hits and six runs. Because of his speed, he sometimes batted in the leadoff spot. Because of his power, he sometimes batted in the middle of the order.
In 61 games, Cain had a .266 average with seven homers, 31 RBIs and 10 stolen bases without being caught.
Center fielder Jarrod Dyson was already limited to pinch-running appearances because of a pulled lat muscle. He hasn't started a game since Aug. 29. Dyson also was hitting well at the time of his injury with a .375 (18-for-48) mark in his a 14-game span. Dyson has 26 stolen bases in 30 attempts.
Hot prospect Wil Myers, now in the playoffs with Omaha, is not likely to be called up. The Royals have indicated they don't want to put Myers on the 40-man roster now because he doesn't need protection from the Rule 5 Draft at the Winter Meetings while other prospects do.
Meantime, Cain is already looking forward to getting healed and in shape for next Spring Training.
"I'll be ready," he said.