Sources confirmed a report by the New York Daily News that Umenyiora could miss up to four weeks, but the defensive end is targeting the Dec. 18 Redskins game for his return.
"He is injured and I can say day to day all I want, but chances are he will not make this one," coach Tom Coughlin said of Umenyiora missing Sunday's game against Green Bay.
Umenyiora suffered a sprained ankle in the first half Monday and did not return in the 49-24 loss to New Orleans.
Umenyiora was at the Hospital for Special Surgery on Tuesday to have his ankle examined by doctors. A source described the ankle as "bad."
The Giants (6-5) enter Sunday's game against the undefeated Packers with several injuries. Running back Ahmad Bradshaw (foot), linebacker Michael Boley (hamstring), linebacker Mark Herzlich (foot), wide receiver Mario Manningham (knee) and safety Antrel Rolle (back) did not participate in a light practice on Wednesday.
Wide receiver Hakeem Nicks also did not practice due to an injury to his ribs and because he arrived to the facility with a headache. The team ran Nicks, who took a huge hit while going for a catch over the middle on Monday night, through the concussion protocol and he was cleared.
Bradshaw said there's "a big shot" that he will return to play Sunday after missing the last four games with a broken foot. He said he wants to save himself during the week and avoid practicing so he can play against Green Bay.
"I feel good," Bradshaw said. "Maybe I'll try to run a little bit this week, see how it feels and then Friday, if I can get out there and practice a little bit, maybe so. I just want to be healthy toward the end of the week, so when Sunday comes there's not a lot of pain and I can rest the bone."
"But I feel good," he added. "I'm planning on playing."
Boley did some agility work and "felt pretty good."
"I'm hopeful," Boley said. "I didn't want to set myself back and have to miss another couple weeks. I'm still taking it slow and see how it goes."
The Giants can use Boley and Umenyiora with their next two games against Green Bay and at Dallas. Their pass rush has struggled in the past two games, registering just one sack against Philadelphia and New Orleans.
The Giants must get pressure on Green Bay's Aaron Rodgers to have a chance to stop a three-game slide. They were not able to sack Drew Brees, who carved up the defense for 363 yards and four touchdowns while running for another.
Umenyiora missed the first three games of the season after having minor knee surgery but is second on the team with seven sacks. Jason Pierre-Paul will start if Umenyiora is out. The second-year defensive end leads the Giants with 10½ sacks and has started seven games this season due to injuries to Umenyiora and Justin Tuck.
The Giants also placed Will Beatty on season-ending injured reserve on Wednesday after the starting left tackle underwent surgery on his detached retina on Thanksgiving.
The team brought back former Giants linebacker and special teams captain Chase Blackburn.
Ohm Youngmisuk covers the Giants for ESPNNewYork.com. Mike Mazzeo contributed to this report.