Ldr oper. was helping change out training roller. Employee tried to pick up roller by himself from the dollie without employee assistance. This resulted in an abdominal strain. Employee felt that he was alright, but he went to the doctor on 5/10, 1 of his 4 days off per his schedule. The Foreman didn't find out that the doctor wanted the employee off for 1 week, until 5/14.