Clifford's high-water mark during his four-plus-year tenure as Hornets head coach came during the 2015-16 season, when he guided the squad to 48 wins.
There is no timetable to Clifford's return, nor will the Hornets have additional comments out of respect for his privacy, the team's statement said. Associate head coach Stephen Silas is coaching the team in Clifford's absence.
Silas joined the Hornets as a scout in 1999 when his father, Paul, was head coach.
Charlotte has a record of 9-13 this season.
Silas has been a longtime assistant in the National Basketball Association, coaching for the Hornets/New Orleans Pelicans (2000-03), Cleveland Cavaliers (2003-05), Golden State Warriors (2006-10) and the Charlotte Bobcats/Hornets (2010-present).