Teixeira suffered a Grade 2 strain of his right hamstring in New York's 10-3 loss to the Rangers on Tuesday, an injury that typically forecasts a recovery time of six to eight weeks. Teixeira would be ineligible to play in the World Series, should the Yankees advance.
"It's extremely disappointing for him and for us," Yankees manager Joe Girardi said. "He's so tough. This is something he can't play through. I know how much he wants to be out there."
Girardi said that Nunez, 23, was selected because he was available and still active playing in Tampa, Fla., where the Yankees had been running a minicamp at their Spring Training complex.
"He was the one guy that we had playing down there," Girardi said. "[Nunez offers] versatility anywhere in the infield if needed and as a pinch-runner."
Nunez hit .280 (14-for-50) with a home run and seven RBIs in 30 games with the Yankees this year. Without Teixeira available, Girardi put Lance Berkman in the lineup at first base for Wednesday's ALCS Game 5 and moved Robinson Cano to the No. 3 spot in the batting order.
"With Robbie, no matter where we've hit him, he's hit and he's produced," Girardi said. "We'll get Robbie more at-bats this way."