Two people spoke to The Associated Press on condition of anonymity because the school has not publicly released any details on Williams. One of the people who spoke to the AP said the severity of the tumor is unknown.
Team spokesman Matt Bowers would only confirm that the 62-year-old Hall-of-Fame coach had a "medical procedure" Wednesday morning.
The news was first reported by WRAL in Raleigh, N.C.
Williams will open practice next month for his 10th season at his alma mater, where he spent 10 years as an assistant to Dean Smith before taking over at Kansas and leading the Jayhawks to four Final Fours. Williams, who has 675 wins in 24 seasons, won NCAA championships with the Tar Heels in 2005 and 2009.
The Tar Heels have won the Atlantic Coast Conference regular-season title and reached the NCAA regional final the past two seasons.
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