Miner states their knee buckled at ~5:30am while dismounting CAT 775 haul truck at end of night shift on 06/11/2017. Miner did not report the incident and went home. Miner called their supervisor at ~4:30pm on 06/11/2017 to report the right knee was swollen. Miner went to local ER diagnosed with knee strain. Miner was released back to work with restriction 06/12/2017.