"It was a noncontact. It just happened into the drop," said Manning, who threw for 292 yards and three touchdowns as the Giants (4-0) won their third road game in a row. "It was the play before the touchdown, where I had Steve Smith deep and threw it a little short."
Manning was replaced by David Carr, but said he expects to be ready for the next game.
"I always assume I'm going to play, that I'm going to be out there," he said. "I've always been a pretty quick healer. I'll be doing everything I can possibly do this week to get healthy and prepared to play Oakland. We'll find out more tomorrow. I can walk around and move around, but there is some discomfort."
Manning seemed to be limping very slightly just moments before connecting with Hakeem Nicks on a 54-yard catch-and-run scoring play that put the Giants up 27-3. A team spokesman said he was not sure which heel was bruised.
Information from The Associated Press was used in this report.