Employee stepped on a rock and rolled right ankle on 1/18. Notified Safety Director at that time and said it was not serious and continued working. Pain did not subside, so saw doctor on 1/30 which discoverd it was a serious ankle sprain. Notified Safety Director of doctor's findings on 1/30. Filled out injury report form on 2/1/06. No lost time as of 2/2/06.