"Currently, there is no timetable for his return", the team said in its statement.
Silas received a text message at about 2 p.m. Monday saying Clifford was too sick to coach the team that evening, the Charlotte Observer reports.
Mueller's Russian Federation investigation cost $3.2M in first five months
Manafort was charged, along with his longtime business partner Rick Gates, for work on behalf of Ukraine unrelated to the campaign.
"(Clifford) is always so prepared for every instance, every game, so today was a lot of study", Silas told reporters before the game. Out of respect for his privacy, the organization did not comment further on his condition. The team said at the time that he was absent due to an illness. The team is 9-13 this season, 11th place in the Eastern Conference.
Silas took over as Clifford's lead assistant upon Patrick Ewing being hired as head coach at Georgetown last 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).