In addition to De Sousa's suspension, which was the stiffest of the four, the Jayhawks' David McCormack received a two-game ban. For Kansas State, James Love will miss eight games, and Antonio Gordon will miss three.
"This kind of behavior cannot be tolerated and these suspensions reflect the severity of last evening's events," Big 12 commissioner Bob Bowlsby said in a statement. "I am appreciative of the cooperation of both institutions in resolving this matter."
De Sousa released a statement Wednesday night on his Twitter account acknowledging that he displayed "highly unacceptable behavior that was a poor representation of my team as well as my own character."
"There is no excuse for my behavior, and I cannot justify the unreasonable choices that I made yesterday on the court," De Sousa said in his statement. "I not only showed a lack of sportsmanship, but I put myself, my teammates and the fans in danger.
"I am truly embarrassed by my actions and have let everyone down who has supported me on my basketball journey. There is no amount of regret that I can express that will correct this mistake. I understand that I am extremely fortunate to have been given the opportunity to play for KU and I recognize that I never should have let my emotions get the best of me, but unfortunately that is what happened. By doing so, I put the Kansas reputation at stake because of a moment of weakness and inconsideration."
De Sousa ended his statement by writing, "I messed up and I am sorry."
In addition to the four player suspensions, both programs were reprimanded by the Big 12 for players' leaving the bench area during the incident, which violates the conference's sportsmanship policy.
Earlier Wednesday, Kansas coach Bill Self indefinitely suspended De Sousa, pending the outcome of the Big 12's discipline.
"Like I said last night, I am disappointed and embarrassed by what transpired because there is no place for that type of behavior in any competition," Self said in a prepared statement. "After meeting with my team and discussing the incident in detail, it is evident that everyone fully understands the magnitude of their actions and all are remorseful for what occurred. We represent the University of Kansas and will all learn from this experience moving forward."
The melee began when De Sousa blocked DaJuan Gordon's shot in the final seconds of an 81-60 Jayhawks victory and then stood over Gordon. At one point during the brawl, De Sousa, who had thrown multiple punches, held a stool above his head before it fell from his grasp as assistant coach Jerrance Howard grabbed at it.
"The players told me they went on the court because they thought the game was over," Kansas State coach Bruce Weber said on Wednesday's Big 12 media teleconference.
It took several minutes for tensions to deescalate and the teams to exit the court. Police officers and coaches from both teams helped break up the fight. Former Kansas star Wayne Simien, an adviser to the team, ran onto the floor to help break up the fracas. Multiple fans were caught in the fight and scrambled to safety.
Kansas (15-3) has played six conference games, which means De Sousa's suspension from the Big 12 will last through the end of the regular season. The Jayhawks are a half-game behind top-ranked Baylor in the conference standings, and they have a team capable of making a deep run in the NCAA tournament.
"Obviously, an unfortunate situation," said Dan Gavitt, the NCAA vice president for men's basketball. "It's a conference game, so it will be up to the Big 12 to determine what actions need to be taken. Other than that, it's too early to say how it might affect them [in the NCAA tournament]."
De Sousa has been at the center of the team's situation with the NCAA, which recently issued a notice of allegations following the forward's ties to an ongoing FBI investigation.
It outlined major violations in men's basketball, levied a head-coach responsibility charge against Self and alleged a lack of institutional control. Those violations are being appealed, and a decision is not expected until after the season.
De Sousa was suspended last season for his role in the case, and he was supposed to sit out this season. However, the school successfully appealed the decision, allowing the junior forward to return to the court.
Kansas and Kansas State meet again Feb. 29 in Manhattan.
ESPN's Myron Medcalf and The Associated Press contributed to this report.