Credit goes to Blair Sanderson over on HawkeyeReport for this:
"NCAA rules state that a player must be eligible at the school he is transferring from in order to be play at his new school. Therefore, this would prohibit Mathieu from playing the 2012 season at any level of NCAA competition. If this turns out to be the reason for Mathieu's dismissal, then the junior's likeliest landing spots are NAIA schools, but HBCU schools and even junior colleges have been mentioned. LSU head coach Les Miles did not disclose the reasoning for Mathieu's dismissal, instead calling it "fundamental behavior."