The two-time Pro Bowl defensive end had arthroscopic surgery on his right knee Friday and likely will miss the Sept. 11 season opener.
The surgery to clean out the knee came just four days after the disgruntled Umenyiora joined teammates at practice for the first time since training camp opened late last month.
"It was better to do it now as opposed to midseason," Umenyiora said in a statement. "It was going to have to be done, the only question was when. If I'm going to miss a little while, I would prefer it be now than at the crucial part of our season. It's the best decision for the team and myself."
Umenyiora, 29, has been in headlines all summer, as he didn't report to training camp with the team following the lockout because he was unhappy with his contract. He alleged that general manager Jerry Reese had promised to re-work the final two years of a contract that was to pay him $7.1 million through 2012.
Umenyiora told The Associated Press on Sunday that he would start practicing Monday, working this season under the terms of his current deal.
Umenyiora's knee became an issue early in training camp, when the Giants announced one day that the nine-year veteran wasn't practicing because he said his knee was bothering him. It led to speculation that the knee had become a bargaining chip.
However, the team cleared Umenyiora to start practicing last week, and he went to Atlanta to receive a second opinion on the knee and was told he could practice.
After three practices -- the team was off Thursday -- the knee needed repair.
"It is a simple debridement," Ronnie Barnes, the Giants' vice president of medical services, said, adding that team physician Dr. Russell Warren performed the operation at the Hospital for Special Surgery in New York.
"He didn't do anything that would cause this to happen, other than it did swell," Coughlin said.
The coach added there is a chance Umenyiora might be ready for the opener at Washington, but that would require a fast recovery.
Reese said Umenyiora told him Thursday that he wanted to have the surgery.
"He told me how much he really enjoyed being back on the field this week, and he's looking forward to getting back out there once he recovers from the procedure," Reese said.
Umenyiora shared the team lead with 11.5 sacks last season and led the NFL with 10 forced fumbles.
In an email to The AP on Sunday, Umenyiora said the Giants offered to put incentives in his contract. But he rejected them as "unacceptable" and said it showed "they don't really respect the fact I sacrifice my health for the franchise."
Copyright 2011 by The Associated Press