Manning was stricken with what coach Tom Coughlin called "a stomach bug" and finished Wednesday working at the team facility. Coughlin had predicted the illness would clear up within 24 hours.
Manning addressed the media Thursday and said he is "100 percent," adding that he "had a full practice today, did everything, took every rep" and felt "good."
He said that on Wednesday, he "just woke up not feeling well," and after trying to "tough it out through meetings" decided he didn't want to "make it worse."
Manning said being able to participate in walkthroughs helped prepare him for the matchup.
"I know the game plan, know what's going on," he said, adding that "the arm felt good today, felt fresh."
Manning said he's "just fortunate (the illness struck) on a Wednesday and not later in the week."
Manning's inclusion on the Giants' injury report Wednesday marked the first time this season that he missed any work.
As expected, running back Ahmad Bradshaw (foot) sat out for the second consecutive day, according to The Star-Ledger. Bradshaw is expected to practice only on Friday, a routine he has adopted in recent weeks since the injury.
The Associated Press contributed to this report.