In a Facebook post viewed by 9News, Nixon made threats to “bury” a serving police officer.
Nixon, 62, was approached by police and arrested near his Port Melbourne home this morning.
He was taken into custody where he is expected to be interviewed by detectives.
Nixon played 63 AFL games between 1983 and 1993 for Carlton, St Kilda and Hawthorn football clubs.
In 1994, he pivoted his career to become a sports agent, later representing some of the biggest AFL stars of all time.
In 2023, Nixon was accused of kneeing a police officer inside a courtroom, where he was appearing on a different assault charge.
Nixon is due to return to count in June over claims he sold fake Melbourne Football Club membership memorabilia signed by players following their 2021 premiership win.