Attorney Lance Unglesby entered the plea Thursday for Jefferson, who was not present for the arraignment.
Jefferson was arrested Aug. 26 and charged with second-degree battery in the Aug. 19 incident. But a month later, an East Baton Rouge Parish grand jury indicted Jefferson on a reduced charge of simple assault, a misdemeanor.
A hearing in the case has been scheduled for May 10.
Jefferson is accused of kicking the alleged victim in the case, Andrew Lowery, during a fight outside Shady's, an off-campus bar in Baton Rouge. Following his arrest, LSU suspended Jefferson for four games.
Lowery's attorney, Michael Bienvenu, said Lowery was knocked unconscious and suffered a broken jaw in the confrontation. He said he expects to file a civil lawsuit in connection with the incident.
Jefferson and teammate Joshua Johns denied involvement in the fight to police. Johns, who also was arrested in connection with the incident, was not indicted by the grand jury.
Unglesby said Thursday that Jefferson looks forward to confronting Lowery's allegations and predicted they will not hold up in court.