O'Hara said the swelling developed Sunday night after he participated in the team's conditioning drills and an afternoon practice.
"It was kind of a surprise to me," said O'Hara, who has been selected to two consecutive Pro Bowls. "I felt good running yesterday, and the next thing you know there was some fluid and some swelling. We are taking it easy right now and trying to get some of it out."
Adam Koets took over at center with the first-team offensive line.
Linebacker Keith Bulluck, wide receiver Hakeem Nicks and tight end Kevin Boss only practiced once for precautionary reasons.
Osi Umenyiora and Justin Tuck were the starting ends in the afternoon workout. Mathias Kiwanuka and Tuck started in the morning. The three are competing for the starting jobs.
Cornerback Corey Webster had a spectacular one-handed interception of an Eli Manning pass pass in the morning workout.
As good as the pick was, the return on the play featured new defensive coordinator Perry Fewell leading the blocking downfield.
"I think he can lead me all the way down the field," Webster quipped.
Fewell has stressed turnovers since replacing Bill Sheridan. New York had just 24 takeaways last season, seven less than its giveaway total.
"Our goal is always to get three or more turnovers a game," Webster said. "Coach is always preaching that. So we've got to live up to that. I think that getting the ball back in our offense's hands, or even scoring on defense, is always a plus for our team as a whole as well as the defense."
Copyright 2010 by The Associated Press