World Cup referee Jaco Peyper has sparked anger after posing for a photo with Wales fans in which he appeared to mimic the elbow that led to Sebastien Vahaamahina's quarter-final red card.
The South African official dismissed the hulking lock in Oita on Sunday after video replays showed him smashing his elbow into the face of Welsh flanker Aaron Wainwright early in the second half with France leading by nine points.
Vahaamahina's shocking rush of blood changed the course of the game and Wales hit back to win 20-19 and book their place in the last four, where they will face South Africa.
But France fans reacted with astonishment after Peyper was seen smiling for the camera alongside beer-drinking Wales fans with his right elbow raised to the chin of one of them, seeming to poke fun at the sickening incident on Sunday night.
There were howls of protests from Twitter users slamming Peyper's judgement, with several calling it "shameful", "disturbing" or "stupid" -- and calling for the 39-year-old to be stood down for the rest of the World Cup or even sanctioned.
World Rugby officials are set to investigate Peyper's embarrassing faux pas but remained tight-lipped Monday.
"World Rugby is aware of a picture on social media of referee Jaco Peyper with a group of Wales fans taken after last night's quarter-final between Wales and France in Oita," World Cup organisers said in a statement.
"It would be inappropriate to comment further while we are establishing the facts."
Serge Simon, deputy head of the French Rugby Federation, retweeted the photo, which has gone viral on social media, with the comment: "If this photo is genuine, it is shocking and explanations are needed."
Vahaamahina was distraught after the match.
Fighting back the tears, the lock told his team mates in the changing room:
"I think I completely lost my head. Frankly it's indefensible."
France boss Jacques Brunel admitted his player deserved to walk after his loss of discipline after what was his last game in charge of Les Bleus.
"I don't dispute the decision," he said. "When you see the images it's very clear he made contact with the opponent's face."
Earlier in the World Cup, Kiwi referee Ben O'Keeffe courted controversy after footage emerged of him offering a "low-five" hand slap during a pool game between Australia and Fiji.
After full-back Kini Murimurivalu had just scored a try to extend Fiji's lead over the Wallabies to 21-12, O'Keeffe extended his right arm and the Fijian duly obliged.
Referees have come under intense scrutiny at this year's World Cup with tournament organisers even taking the rare step of rebuking match officials for their performance in the early stages.
Inconsistent interpretation by referees of new guidelines over high tackles had led to confusion and dismay from coaches and players, but before the quarter-finals World Rugby chief Bill Beaumont insisted that standards had improved.