Lionel Messi was spotted telling the referee to 'speak to me with respect' in a heated exchange during Argentina's clash with Switzerland this morning.
The incident occurred during the 42nd minute of the South Americans' 3-1 victory over the Swiss when Messi confronted Portuguese official Joao Pinheiro.
The pair's conversation was picked up by broadcasters and, in a moment which went viral on social media, the Argentinian captain was heard telling the referee: 'Speak respectfully, don't be disrespectful. Speak to me respectfully. I spoke to you respectfully.'
It came with the Argentinians 1-0 up on the brink of half-time in Kansas City thanks to an early header from Alexis Mac Allister.
Switzerland later hit back when Dan Ndoye burst in behind and side-footed an accurate effort past Emi Martinez into the bottom corner.
But - after Breel Embolo was dismissed for a dive - the world champions were dominant against 10-men as the game neared its close. Julian Alvarez restored their lead with a sumptuous strike from distance before, with just seconds left, Lautaro Martinez made it 3-1.
The result, however, sparked controversy as Switzerland took aim at the referee for his decision to send Embolo off on 72 minutes.
The striker was shown a second yellow card after a video assistant referee review which led to him being adjudged to have dived - rather than being fouled by Argentina's Leandro Paredes. A new rule introduced for this World Cup states that if a player is booked or sent off - but the foul was actually committed by the opposition - the decision can be changed.
Switzerland's response was emphatic. Defender Manuel Akanji said: 'Every little thing was called against us' and 'I've never experienced such a one-sided game.' Manager Murat Yakin called the refereeing 'incomprehensible'.
Their comments only add to the outlandish World Cup 'fixing' conspiracy theories which suggest Messi and Co are being favoured by FIFA to knock out England and lift the trophy in New Jersey next Sunday.
Egypt, who lost to Argentina in the last round, have already called for a FIFA investigation over the manner of their exit. Their winger Mostafa Ziko said: 'This tournament has been fixed,' while coach Hossam Hassan said: 'This match was rigged, and the whole world saw it.'
FIFA's chief refereeing officer Pierluigi Collina responded, stating that 'nobody can question the integrity' of the refereeing and 'unfounded allegations have no place in our sport'.
FIFA president Gianni Infantino then said: 'Tonight, I suffered with Argentina…but I’m neutral.'
Ex-Man City defender Akanji, however, later accused the Portuguese official of 'being against' him and his team-mates.
He fumed: 'Every little thing was called against us. Every dive and every foul by the Argentinians went unpunished. I don't usually say anything against the officials, but I've never experienced such a one-sided game as today.
'As soon as the game was over, I thought: I'm so proud of our team. What we've achieved throughout the entire tournament, and especially today... We played against the world champions, and they didn't stand a chance.
'I can't recall a single scoring opportunity from open play where we were lucky. If the game had continued 11 against 11, it would have likely gone in our favour.'
The result means Argentina will now face England in a World Cup semi-final on Wednesday in Atlanta after the Three Lions overcame Norway earlier in the night.
And speaking after the Argentinian quarter-final, Messi sent a message to England ahead of what will be a huge clash.
He said: 'Everything I have seen and remember [about Argentina vs. England from 1986] is from videos and images that Argentinians constantly watch and relive.
'But I think this group is used to playing football matches regardless of the opponent. Obviously, playing against England is special because they are a powerhouse, and matches against powerhouses are always special.
'Personally, it's the first time I'm going to play against them. I've played against everyone except England, so it will be nice for that reason too.
'And we'll experience it for what it is: a World Cup semifinal against a powerhouse, a great team, and we'll try to arrive in the best possible shape to compete again.'