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Matt Slocum, File, Associated Press
FILE - In this March 5, 2012 file photo, New York Yankees' David Robertson throws during a spring training baseball game against the Philadelphia Phillies, in Clearwater, Fla. The Yankees took their first misstep of 2012 when All-Star setup man David Robertson sprained his right foot when he fell down stairs while moving boxes in his spring training home.An initial X-ray was negative, and the reliever was taken a hospital for an MRI Thursday, March 8, 2012.

TAMPA, Fla. — David Robertson walked out of the Yankees clubhouse, holding a pair of crutches, his right foot in an oversized black boot.

Instead of making his second spring training appearance, he had gone to a hospital Thursday for an MRI after a household accident: He sprained a foot when he stumbled on stairs while moving boxes.

"It's embarrassing. I already had Mo rag me out about it," he said after speaking with closer Mariano Rivera.

The New York Yankees were waiting to find out the cost of their first misstep of 2012. An initial X-ray on the All-Star setup man was negative, and Robertson awaited the results of the MRI.

Manager Joe Girardi said the initial diagnosis was a mid-foot sprain.

"'I'm concerned," Girardi said. "It hurt him to walk, (and) you assume that he's going to be down a little bit of time even if everything comes back OK. Now that doesn't mean he wouldn't have time to get ready for the season. But you've got to start over a little bit."

Robertson was hurt Wednesday night at his home in St. Petersburg. He picked up two empty boxes, one inside the other, and walked down the stairs.

"I just misjudged one step and just caught it funny, and it just kind of rolled under me," he said.

He understands that some may think there's more to the story, that the injury couldn't be caused by a tumble at home.

"I can tell you right now that's the truth," he said. "My wife was like, 'What are you doing down there?' She saw me laying there on my foot."

Robertson said his foot started throbbing an hour or two later but he applied ice and it felt better in the morning. Girardi said if Robertson were sidelined for two weeks or less, he still could be ready for the Yankees' opener at Tampa Bay on April 6.

"If it's going to happen, let it happen now," Girardi said.

Robertson had a breakout season in 2011, going 4-0 with a 1.08 ERA in 70 games and becoming the Yankees' primary setup man.

"Last year, he did a tremendous job," Rivera said. "So we're expecting something good out of him this year, also."

If Robertson isn't ready for opening day, Rafael Soriano likely would move up to New York's eighth-inning pitcher.

New York has bad memories of pitchers and injured feet. Chien-Ming Wang sprained his right foot while running the bases at Houston on June 15, 2008, and missed the rest of the season. Wang struggled to a 1-6 record with a 9.64 ERA when he returned the following year. He needed shoulder surgery that sidelined him until last July, when he came back to the major leagues with the Washington Nationals.

For now, the Yankees were hoping Robertson makes a speedy recovery.

"They weren't even heavy boxes," Girardi said. "I told him to kick them down the stairs the next time."

Notes: Rivera threw 32 pitches in his second batting practice session. He likely will make his exhibition debut Sunday.