South Africa captain Siya Kolisi controversially escaped a ban on Monday despite headbutting Scotland's Peter Horne during the Springboks' 26-20 win against Scotland.
TV footage appeared to show Kolisi's head making contact with the head of Horne as he tried to extricate himself from being pinned to the floor by the Scotland centre in a pulsating encounter in Edinburgh on Saturday.
A statement from global governing body World Rugby said Kolisi, 27, had received a warning from citing commissioner David Pelton for striking with the head during the match at Murrayfield but that the offence did not merit a red card.
"Having reviewed the video angles, the citing commissioner determined that there were mitigating factors which meant that the action did not meet the red card threshold, including the player being illegally prevented from rejoining the play by Scotland's Peter Horne and the moderate force of the strike to the side of the head," it added.
"The match officials did not see the incident at the time on the field of play."
A citing commissioner warning is issued for offences falling just short of a red card and forms part of a player's disciplinary record.
South Africa play Wales on Saturday in the final match of their European tour. They narrowly lost to England but beat France and Scotland.