Is Mariano Rivera's career over after tearing ACL?

(CBS/AP) KANSAS CITY, Mo. - Mariano Rivera drifted back to the outfield wall, just like he'd done in batting practice so many times before, baseball's greatest closer tracking down another fly ball with childlike joy.

Everything changed before anybody could blink.

The Yankees' 12-time All-Star caught his cleat where the grass meets the warning track in Kansas City, his right knee buckling before he hit the wall. Rivera landed on the dirt, his face contorted in pain, as Alex Rodriguez uttered the words "Oh, my God" from some 400 feet away.

Bullpen coach Mike Harkey was the first to reach Rivera, whistling toward the Yankees' dugout for help. Manager Joe Girardi had been watching from behind the batter's box and set off at a run down the third-base line, angling toward center field and his fallen reliever.

"My thought was he has a torn ligament, by the way he went down," Girardi said later.

His instincts proved correct.

Rivera was diagnosed with a torn ACL and meniscus Thursday night after an MRI exam taken during the Yankees' 4-3 loss to the Royals. The injury likely ends his season, and quite possibly his career, an unfathomable way for one of the most decorated pitchers in history to go out.

"It's not a good situation, but again, we've been through this before, and we're being tested one more time," Rivera said, pausing to compose himself in the Yankees' clubhouse. "It's more mentally than physical, you know? You feel like you let your team down."

CBSSports.com baseball insider Jon Heyman says Rivera is said by intimates to still be of a mind to try to make it back to pitch this season despite the long odds. And already, there are small signs he believes he can buck conventional wisdom and medical history and do it. Derek Jeter told Yankees writers he spoke to Rivera and predicted of the all-time great, "He'll be back.''

The 42-year-old Rivera has said that he'll decide after the season whether hang it up after 18 years in the major leagues. And while Girardi said he hopes that baseball's career saves leader makes a comeback, Rivera sounded as if retirement is a very real possibility.

"At this point, I don't know," he said in a whisper. "Going to have to face this first. It all depends on how the rehab is going to happen, and from there, we'll see."

The injury seemed to cast a pall over the Yankees, who played from behind the entire way Thursday night. They put the tying run on third base in the ninth inning before Mike Moustakas made a stellar play on a chopper by Rodriguez, throwing him out by a step to preserve the win.

Afterward, the only thing on A-Rod's mind was Rivera.

"I saw it all go down," Rodriguez said. "It's hard even to talk about it tonight. I mean, Mo has meant so much to us on a personal level, and his significance on the field, on the mound. But the bottom line is we're the New York Yankees, and nobody is going to feel sorry for us."

There's a much different feeling about Rivera, though. One of the most durable pitchers to ever play the game is well-liked and universally respected.

That's what happens when you save 608 games and have five World Series rings.

"You're talking about somebody who does something that's never been done," said Derek Jeter, who had four hits in the game. "It's not like somebody comes along the next day and does it."

Jeter said that Rivera has been shagging balls for "20-some years," at least as long as they've known each other. It never crossed the captain's mind that Rivera would get hurt tracking down a fly ball in batting practice. It's just something that people had come to accept.

"That's his conditioning. He's always shagging balls," Jeter said. "He's like a center fielder anyway. It was a freak thing. There's no other way you can explain it."

Girardi also defended Rivera's decision to shag balls in batting practice, pointing out that the reliever hadn't been on the disabled list since 2003, and reasoning that Rivera may never have become the same shutdown closer if not for all the work he put in before games.

"You have freak injuries, and this is one of them," Girardi said. "We had a guy carrying a box down the stairs that broke his foot. You can fall off a curb. You have to allow him to be an athlete and a baseball player and have fun out there. I've never seen Mo do anything recklessly, or seen Mo dive to try to rob a home run. It's the way he exercises."

Girardi was too far away from the outfield wall to see what happened, but he knew that Rivera had sustained a significant injury when he saw players and coaches gathering around him.

Rivera grabbed immediately at his right knee and started rubbing it, stopping only to briefly cover his face with his glove. Harkey and Girardi eventually carried Rivera to a cart brought onto the field, gently setting him into the back with his knee propped up.

"At first I thought he was being funny, but then I realized that he was injured, he was down, and that's when I really got worried," said David Phelps, who made his first major league start Thursday night. "There's nothing I can do but stand there and watch. It's a miserable feeling."

The cart rounded the warning track before disappearing up a tunnel, and Rivera didn't put any weight on his knee when he was helped back into the Yankees' clubhouse.

He was examined by Royals associate physician Dr. Joe Noland, but it wasn't until the MRI exam was taken at KU MedWest that head physician Dr. Vincent Key made the diagnosis.

"I thought it wasn't that bad, but it's torn," Rivera said. "Have to fix it."

Girardi said that Rivera would be reexamined by the Yankees' physicians, but Rivera said that he would rather remain with the team in Kansas City than fly back to New York on Friday.

The Yankees play three more against the Royals before a day off.

"If it's going to happen, it's going to happen doing something I love to do. And shagging I love to do," Rivera said. "I'd do the same thing, without hesitation. The reasons why it happen, you have to take it as it is. Fight through it. You know, just have to fight."

Rivera is only the latest closer to go down with a significant injury this season.

The Royals' Joakim Soria, the Reds' Ryan Madson and the Giants' Brian Wilson all required Tommy John surgery. Tampa Bay's Kyle Farnsworth is out with a strained elbow, Boston's Andrew Bailey had surgery to repair a ligament in his right thumb, and Washington's Drew Storen had a bone chip removed from his elbow, though the Nationals expect him to pitch this season.

Of course, none of those players has nearly the pedigree of Rivera.

With the same devastating cutter that has carried him for years, Rivera has made at least 60 appearances each of the last nine seasons. He blew a save on opening day this year, but allowed only two hits in eight scoreless innings after that, picking up five of his 608 saves.

"I always argued he was the best pitcher of all-time," first baseman Mark Teixeira said. "Not just the best reliever, but the best pitcher of all-time.

"Accidents happen. That's all I can say. You can get hurt getting out of bed, literally. You can get hurt doing anything," Teixeira said. "That's Mo. Part of what makes him great is he's so athletic, and he loves to run around out there and have fun. You can't play this game for 15-plus years without having fun. It was just a tough accident."