A source close to each veteran told the Associated Press on Tuesday that the team told the players they would be cut on Thursday in what are salary-cap moves.
The Giants might also cut another offensive lineman on Thursday. Tackle Shawn Andrews, who played in 13 games and started seven last season, tweeted that he and the team failed to rework the six-year, $32-million contract he signed last year.
Andrews also tweeted that things weren't over, but that might mean his career more than his time with the Giants.
The Giants are roughly $10 million over the NFL's new $120.4 million salary cap. The releases of O'Hara ($3.45 million in 2011) and Seubert ($2.25 million) will reduce the problem by roughly $6 million. Andrews made $1.5 million last season.
O'Hara, 34, who was the starting center since 2004, was limited to six games last season because of ankle and foot injuries. He had surgeries on both in the offseason.
O'Hara, who played at Rutgers and is a local fan favorite, has been the Giants' player representative in recent years and he voted in Washington on Monday on the agreement that ended the 4½-month lockout.
The 32-year-old Seubert probably was the Giants' most valuable lineman last season. He moved from guard to center after both O'Hara and backup Adam Koets were sidelined.
However, Seubert suffered a major knee injury against Washington in the final game of the season when he dislocated his right knee. It was his second major injury. He broke his right leg in a game against Philadelphia in 2003 and did not return until the 2005 season. He needed five surgeries to repair the leg.
It was uncertain whether either O'Hara or Seubert would have been ready for the season, anyway. The Giants could re-sign them, but it is not known, at this point, if either wants to come back.
The moves leave Koets as the only returning center with starting experience, and he also is coming off a major knee injury.
The Giants open the preseason on Aug. 13 at Carolina.