The incident occurred in the third quarter of the match, in which Houston triumphed 105-103, when both players got involved in a tussle and Harden ended up falling down. He then proceeded to kick his foot up and into James' groin region.
Harden was initially hit with a flagrant 1 foul for kicking James, but the league upgraded it to flagrant 2. If the referees had decided to slap Harden with a flagrant 2 foul during the match, he would have been ejected from the game immediately.
Following the match, a rather infuriated James said that Harden's actions were "not a basketball play" and that the league would look into the matter.
James would have been frustrated with himself as well as he missed two vital free throws with just over four seconds left in overtime, which allowed Houston to escape with their fifth straight win.
Harden, who is the NBA's leading scorer and a candidate to win the Most Valuable Player award, will watch his side take on the Atlanta Hawks at the Phillips Arena on Tuesday from the sidelines.