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03/24/2013 7:08 PM ET

Improved defense has Nunez ready to play shortstop

TAMPA, Fla. -- With Derek Jeter expected to miss his first Opening Day since 2001, the Yankees are ready to entrust Eduardo Nunez with a starting role at shortstop until the captain is able to return.

Yankees manager Joe Girardi said that he has been pleased with what he has seen from Nunez, who went 2-for-3 with a run scored and an RBI triple in New York's 7-6 win over the Rays on Sunday.

"He's worked very hard on his defense, he's swung the bat well, he's run the bases well," Girardi said. "He provides a speed option that we really didn't have last year a whole lot. You get him and Gardy [Brett Gardner] in the lineup, and it could create some problems."

Nunez joked this week that he has not been throwing as many balls in the stands behind first base this spring, but that has not been by coincidence.

Nunez has been working with infield coach Mick Kelleher on his arm action, something he showed off on a fourth-inning play Sunday. Nunez whirled behind second base on Shelley Duncan's grounder up the middle, throwing accurately on a bounce to first baseman Juan Rivera, who did not scoop the infield hit.

"He's bouncing it there on purpose," Girardi said. "It's on the money, and it's a good throw. It does show you what kind of progress he's made. That's one of the things he's worked on. He went and worked with Mick on that play."

Mo dealing with migraines, but Yanks not worried

TAMPA, Fla. -- Yankees closer Mariano Rivera has been dealing with severe migraine headaches this spring, but the team does not believe that the issue is serious.

Rivera said that he was feeling better when asked about the headaches on Sunday, which were first reported by the New York Post.

"Everything is fine. I'm good," Rivera said. "When it comes to my head, I'm worried. I have to check. I don't like to feel headaches. I just wanted to know what it was; I wanted to know what was going on."

The Yankees sent Rivera for a CAT scan and blood test as a precaution.

"We're not worried at all," Yankees general manager Brian Cashman said. "We have to follow certain protocols. He mentioned he was having some migraines, so there's a fire drill you have to run through just to be cautious.

"So we did that, expecting the results to be negative, and they were. So there's no issues. He might have the migraines, but they're not anything. All those tests were good."

Bombers bits

• Yankees outfielder Brennan Boesch (sore left rib cage) is "feeling good," according to Cashman. Boesch told the team that they were being "overly cautious" in holding him out of action on Sunday, but he could return to play on Tuesday.

• Cashman said that he has been impressed by the work ethic shown by first baseman Mark Teixeira (strained right forearm), who has been working out in the gym at George M. Steinbrenner Field as he hopes to rejoin the team in the middle of May.

"He's a monster," Cashman said. "He's going through all this different stuff with his legs and his arms. He's making sure that whatever he can do while being down because of the wrist or the hand, that he can close the gap as best he possibly can on every other aspect."

• The Yankees announced that infielders Walter Ibarra, Addison Maruszak and Jose Pirela have been reassigned to Minor League camp.

Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch and read his MLBlog, Bombers Beat. This story was not subject to the approval of Major League Baseball or its clubs.