The Miami Herald reported Thursday Williams could miss most of the 2004 season.
In a statement, the school said, "Williams will start rehabilitation immediately and will be re-evaluated in eight to 12 weeks."
The surgery prevented him from attending the first day of classes Wednesday.
Williams was a Parade All-American last season while playing for Miami Carol City High School. He was called by some analysts the best scholastic linebacker in the nation.
He was a controversial signee because of his extensive criminal record. The Palm Beach (Fla.) Post reported a recruiting trip to the University of Florida in Gainesville in late January resulted in several criminal charges against him. He then was arrested in Broward County for violating probation. He was placed on three years' probation in July, and was admitted to UM under a list of conditions he must comply with to keep his scholarship.