The team announced that Umenyiora is not practicing "because he says he has a sore knee."
Umenyiora has an issue with his meniscus, which can be managed and does not require immediate surgery, a source confirmed. The Wall Street Journal first reported the injury.
Umenyiora, who is mired in a contract dispute with the Giants, could opt for surgery, which would likely take four to five weeks of recovery time, according to a source.
Umenyiora has not practiced since joining the team Saturday.
Umenyiora missed the entire 2008 season with a left knee injury, which required surgery to repair a torn lateral meniscus, but the source said his current issue is unrelated.
He also underwent surgery on his hip this offseason but coach Tom Coughlin said that was not the reason why he wasn't practicing. Umenyiora said in June that his hip was fully recovered.
Umenyiora wants a new contract or to be traded. In 2005 he signed a seven-year, $41 million extension, including $15 million guaranteed. He has two years remaining on that deal at a total of just over $7 million in base salary.
On Monday, Umenyiora's agent was given permission to seek a trade with a team willing to part with a first-round pick. But by Wednesday, the team had rescinded permission given to agent Tony Agnone. Umenyiora met with GM Jerry Reese and was excused from Wednesday night's practice to "clear his head," according to a source.
But Umenyiora attended the practice, watching from the sideline.
A source says Umenyiora believes that the Giants could have traded him this week if they were willing to lower their price from a first-round pick.
"I hope there is a chance," Umenyiora told The Associated Press in an email earlier this week when asked if there's any chance he can work things out with the Giants. "But who knows. What really annoys me is the hypocrisy of people clamoring for my head for asking for a new deal or to be traded."
In a sworn affidavit as part of the recent Brady v. NFL antitrust lawsuit during the lockout, Umenyiora said Reese told him in 2008 that if the defensive end were still playing at a high level in two years, he'd reward him with a new contract or trade him to a team that would pay him like a top-five defensive end.
The Carolina Panthers recently agreed to terms with Charles Johnson on a contract worth $72 million over six years, including a $30 million signing bonus. Umenyiora wants a raise and is frustrated with people who are criticizing him for wanting a new contract.
"How does a guy who had one good year -- no disrespect to Charles Johnson -- sign a deal and make more than both me and (Justin) Tuck combined? It's not right," Umenyiora said in the email. "Everyone in this business understands that is exactly what it is. Business. And just like none of us get upset when our teammates are released due to business decisions, the teams also don't get upset when something like this happens. It's just frustrating to see how people react to one thing, and not the other. Just be fair."
Meanwhile, the Giants suffered their first major injury of the season when cornerback Bruce Johnson suffered a ruptured Achilles tendon early in practice.
Ohm Youngmisuk covers the Giants for ESPNNewYork.com.