Clark, a 6-foot-8 sophomore forward from Putnam City High School, has been ruled academically ineligible and will not be with the Sooners for the rest of the season, it was announced on Thursday.
Clark will not be enrolled at OU during the second semester, though it's uncertain what his future plans are.
"It's a big loss for us," Oklahoma head coach Jeff Capel said in a statement released by the university. "But my concerns about how this situation affects our team are far outweighed by my concerns about how it affects him personally."
Clark, who was late meeting NCAA academic standards before his freshman season, missed the entire Big XII schedule last year after suffering a season-ending knee injury in late December.
Clark averaged 5.4 points in 14 games so far this year, but had two of his best showings of the season in Oklahoma's wins at West Virginia and at home against Rice.
"Keith was playing very well," Capel said.
Clark was on the bench but not suited up during Monday's win over Mount St. Mary's.
"He's one of our most talented players and he's a good kid and a great teammate," Capel said. "We're going to miss him."