To fill his spot on the active roster, the Yankees called up Brandon Laird from Triple-A Scranton/Wilkes-Barre. Laird was expected to arrive before first pitch at 7:10 p.m. ET, but his flight was delayed, so he was deemed inactive.
Girardi wasn't sure how long Pena would be out.
"I mean, we put him on the 15-day DL knowing it would be that long," Girardi said. "I've heard guys try to come back [from appendicitis] after five or six days. I think that's a little bit difficult. But I wouldn't expect it would be too long."
Several players have undergone emergency appendectomies in recent history, with the Cardinals' Matt Holliday and the White Sox Adam Dunn each undergoing the procedure in April.
Dunn missed only six games and Holliday was out for seven. But then there are players like Padres starter Aaron Harang and Brewers outfielder Corey Hart, each of whom missed about five weeks because of it in 2009.
Pena's appendectomy was the second by a Yankees player in the last two weeks. Right-hander Joba Chamberlain -- out for the year because of Tommy John surgery -- recently had one as well.
Regardless of how long Pena is out, it's another injury blow to what has become a thin position for the Yankees.
Alex Rodriguez isn't expected back until possibly early September after undergoing arthroscopic knee surgery. With him out, Eduardo Nunez has been getting the bulk of the playing time at the hot corner. But Pena was a valuable asset off the bench because of his ability to play second base, third base and shortstop.
"You lose some flexibility, definitely, because you had two guys who could do that," Girardi said. "Now you have one, and the other guy [Nunez] is more of a third baseman [for now]."
Pena was 2-for-25 while appearing in 14 Major League games this season, but provided solid defense and made some nice plays while getting the start at third base in Sunday's win over the Blue Jays.
Laird, a 23-year-old right-handed hitter -- and the brother of Cardinals backup catcher Gerald Laird -- was hitting .266, with 10 homers and 49 RBIs in 90 Triple-A games. He also has experience playing first base, but that won't be necessary on the big league club.
"It's a young man who had an excellent year in Double-A," Girardi said. "[Laird] started off a little slow in Triple-A, but has really turned his season around, and we have high hopes for this kid of being a prospect."