Head coach Tom Coughlin said Manningham will not practice and will undergo further testing to gauge his availability. Manningham underwent a test Wednesday morning before he was held out of practice.
Manningham told the Giants of his injury after Sunday's loss to the Titans. Coughlin was surprised by Manningham's revelation, which puts his status for Sunday night's home game against the Chicago Bears in doubt.
"He really appeared to be fine Monday when we saw him," said Coughlin, who will move Victor Cruz to the third receiver spot if Manningham cannot play. "We didn't expect there would be any slowdown in his performance today. There was. So hopefully we can do the test again and see how that comes out. We are a little bit surprised that there is an issue."
"Mario has done really well, has had some big plays for us, a number of balls down the sideline, third-down conversions, all sorts of stuff," quarterback Eli Manning said. "He has really grasped the offense a lot better.
"We got to see how the week goes. Hopefully we will have Mario back tomorrow. If not, Vic has got to step up and make some plays for us."
Coughlin also said center Shaun O'Hara is still sidelined due to his ankle/Achilles injury. Coughlin has said he thought O'Hara would need about two weeks of recovery, but the coach isn't sure now.
O'Hara sat out against the Titans and did not practice at all last week. The center saw a specialist earlier this week about his injury.
"We are hoping it is not a surgical issue," Coughlin said.
"Hopefully we will get them both [practicing] tomorrow," Coughlin said.