He will miss the rest of the regular season and perhaps all of the playoffs.
Van Horn, the primary backup for Dirk Nowitzki, was injured Friday night while trying to make a steal. He is averaging 8.9 points, 3.6 rebounds and 20.4 minutes per game but has played only 53 games because of injuries. He'll be a free agent after this season.
Because of several other injured players, the Mavericks have asked the league for a roster exemption that would allow them to carry a 16th player.
"We think our chances are not good," coach Avery Johnson said.