EE stated they slipped getting off D8 CAT dozer at the gravel pit and twisted a knee. No witnesses to this accident, and EE didn't report this to a supervisor at any time. I was notified of the incident when EE filed first report for workman's comp on 5/12/17 with HR. People did see EE limping and asked about it, but EE didn't report this to anyone. Date & time are in question.