KANSAS CITY — Yankees closer Mariano Rivera was carted off the field at Kauffman Stadium on Thursday after appearing to suffer a right knee injury shagging fly balls during batting practice.

The Yankees were hitting on the diamond just after 7 p.m. ET as Rivera raced back, reaching up for a fly ball. His right knee buckled near the warning track and he crumpled to the ground near the fence, rubbing his knee immediately in pain.

Teammates and coaches crowded around in concern as Rivera received attention in the outfield. Manager Joe Girardi was among those watching the all-time saves leader be propped onto the back of a flatbed truck and driven around the warning track.

Head athletic trainer Steve Donohue was riding with Rivera, who was gingerly helped into the clubhouse and did not appear able to put pressure on his injured leg.

No further information was immediately available about Rivera’s injury. Rivera regularly shags fly balls in center field during batting practice and has spoken about hoping to play the position in a game before he retires.

(… And he doesn’t want to say what it is … but he might have anyway.)

Mariano Rivera just spent about nine minutes talking to the media at Steinbrenner Field, saying that he has made a decision about whether or not he will continue to pitch in 2013.

Rivera danced around it as much as he could, saying several times he wouldn’t reveal the decision, but it was impossible not to come away from that chat thinking that Rivera has already decided 2012 will be his final season.

In fairness, Rivera has hinted at retirement before, but he said that nothing – “Even if I save 90 games. Even if they want to pay as much money as they want to,” he said at one point — can change this particular decision. So what else could it be?

“How many times have I told you guys that this is my last year?” Rivera said. “Seven, eight years? I keep telling guys, after this year, I’m not going to play [any] more. Then there it is, I play two more years, a contract for three more years. Then another three more years. Yes, I have. … But this one is different. This is it. This one is my decision. When I let you guys know what it is, you guys will know.”

Rivera was asked if he sees himself staying in baseball after he does retire. He said that he does, but not at the big league level – he’d prefer to be in the Minor Leagues working with younger players. And managing? That’s completely out, he said.

“No, no, no,” Rivera said. “If I wanted to be a manager, I’d continue playing until I can’t [any] more. Because you have to do the same things, traveling and traveling, doing all that stuff. I’d have to come to Spring Training. No, no managing. That’s out.”

All this talk about Mariano Rivera got me wondering — he’s always said that he would love to play center field in a game, whether it’s for one inning, a batter, whatever.

Today at Safeco Field, Joe Girardi laughed at the topic and acknowledged that seeing No. 42 in center field someday is actually a possibility.

“I’ll think about that when he tells me that he’s near the end,” Girardi said. “It’s something I would definitely think about. That’ll get me in trouble.”

Of course, with concerns about injuries, there’s really no perfect time to do such a thing. Even if the Yankees clinch the division and it were Rivera’s final season, you’d still want to keep him healthy for the postseason. It might take a 2008-esque playoff miss to make it happen.

Then again, Girardi did put Jorge Posada at second base this year without incident. Rivera shags fly balls in center field every day during batting practice and the Yankees say – without a hint of humor – that he’s one of the best athletes out there.

“Maybe I’d try to do it for one hitter; a guy that hits ground balls or strikes out,” Girardi said. “And there would be nobody on base where he’d make a throw.”

Mariano Rivera was just about as angry as I’ve ever seen him after tonight’s game, saying that the umpires’ ruling on Billy Butler’s third-inning solo homer cost the Yankees the game.

“What I saw wasn’t what they saw,” Rivera said. “Obviously, given the other team, they saw the same thing. What I saw wasn’t that the ball hit the back wall or something like that. It came down flat on the edge of the corner and ricocheted back out.

“It didn’t hit the wall. But nobody know’s what’s the rule. I assume that’s still in play, everything. That you need to clear the fence to hit a home run. To me, matter of fact, the ball never hit the back wall. That’s why they assumed it hit it, and they called a home run. But what I saw, it wasn’t.”

Rivera said that the fact that Butler was spotted in the dugout holding his helmet, as though he was ready to go back to second base, was evidence the call was muffed.

“I mean, that cost us the game. Tie game, you know?” Rivera said. “I understand we’re human, but come on. You have replays, and get the call wrong? That’s unacceptable.”