KANSAS CITY, Mo. (AP) — 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.”

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.

Derek Jeter said that Rivera has been shagging balls for “20-some years