"It wasn't anything serious," Self told ESPN. "He'll probably miss a week."
On Thursday, Ellis was officially ruled out for Saturday's game at Oklahoma.
Ellis played 17 minutes in Kansas' 76-69 home victory against West Virginia on Tuesday night before teammate Landen Lucas fell on his leg late in the first half. Ellis underwent an MRI, which showed a sprain.
He is averaging 14.2 points and seven rebounds for the Jayhawks, who clinched the outright Big 12 regular-season title with the overtime victory over the Mountaineers.