"It's tough, because he's a great kid with a great work ethic that's willing to do anything for you -- that provides a lot of excitement. But for his development, we thought it was more important to get him playing every day at short again."
Nunez had made a team-leading four errors in 20 games for New York this year, appearing at shortstop, second base, third base and in the outfield. Last year, he committed 20 errors, 14 at shortstop and six at third base.
"The majority of it is probably just from not being comfortable," Yankees captain Derek Jeter said. "I don't want to speak on his behalf, but I would assume just not playing every day is tough to do. ...
"He needs to play. That's the thing. Everyone would love for him to be here, but he needs to play. That's the best thing for him."
The Yankees were willing to take a chance on the 24-year-old because of a promising bat, and Nunez had two hits with a walk on Thursday to raise his average to .294 (15-for-51). But his inconsistent defense was too much of an issue at this time.
"Our thought is that this kid is going to be an everyday shortstop," Girardi said. "That's what, for the most part, we want him to concentrate on. We think that that is where his true value is probably going to be.
"Time will tell, but this kid -- we've seen when he's played shortstop on an everyday basis, how things seem to smooth out. It's not easy what we were asking him to do, especially a young man who had never done that in his career."
With Nunez sent to Triple-A, Jayson Nix will be the Yankees' primary backup for Derek Jeter and Robinson Cano at shortstop and second base, respectively. Eric Chavez, who was activated from the seven-day concussion disabled list on Friday, will back up at first base and third.