Bradshaw was released from the Abingdon (Va.) Regional Jail on Sunday after serving most of a 30-day sentence. The league is investigating whether the player, who helped the Giants win the Super Bowl as a rookie, violated its player conduct policy.
Charles A. Stacy, Bradshaw's attorney, said the underlying charge for which Bradshaw was placed on probation stems from an offense that occurred while Bradshaw was a juvenile.
Bradshaw was recruited by and originally enrolled at Virginia, but was dismissed from the football team without playing a game after pleading guilty to resisting arrest and underage drinking, both misdemeanors, and being placed on probation.
He rushed for almost 3,000 yards and 31 touchdowns in three seasons at Marshall after joining the team as a walk-on, but had another arrest for allegedly stealing a PlayStation 2 video game.
He pleaded guilty in that case to misdemeanor petit larceny and was given two years probation. A 12-month jail sentence was suspended.
Bradshaw was a key player in the Giants' three playoff victories and their Super Bowl win against the New England Patriots last February.