"We're going to see how this works," Girardi said.
A former catcher, the 39-year-old Posada has been the Yankees' primary designated hitter this year against right-handed starters. But Girardi had Eric Chavez as the DH against Red Sox righty Josh Beckett.
"It's very disappointing. You want to be out there," Posada said. "But right now it's about winning ballgames. He told me he wants to put the best lineup out there."
Posada is just 3 for 18 this month and is hitting only .230 overall with nine homers and 31 RBIs. Chavez, who was activated from the 60-day disabled list on July 26, is batting .323.
Said Girardi: "We think Jorge's going to be a big part of the team. He was disappointed. You could see it."
It's not the first time that Posada's lack of production has affected his spot.
In June, Posada asked out of the lineup when he was dropped to ninth in the order in a game against Boston in New York. Posada apologized the next day.
"He's just struggled to find a way to get his hits," Girardi said. "It's just been a tough year for him. ... Jorgie and I have a relationship. That has gone a long way."
Girardi said he'd stick with Chavez and Eduardo Nunez, who again filled in for injured Alex Rodriguez, for the time being. Girardi added Posada's spot on the roster is safe when Rodriguez likely returns from the disabled list later this month.
"This is today," he said. "I can't tell you what it'll be two weeks from now."