Arenas, 22, who signed a six-year, $65 million contract with the Wizards in August 2003, said in a statement released by the team that he had maintained the needed registration in Arizona, but
failed to do so while living in California. Arenas formerly played for the Golden State Warriors.
Arenas averaged 19.6 points a game in his first season with Washington and will miss the team's Nov. 3 regular-season opener against the Memphis Grizzlies.
"It was an oversight on my part," Arenas said in the statement. "I have dealt with the situation and I'm moving forward."
Arenas was taken out of the starting lineup for the final two games last season, first for missing a team flight to Detroit, then for being late to a morning shootaround.
Arenas also missed a shootaround last season because he was shooting pool in the player's lounge in January.