The Uruguayan forward is accused of sinking his jaws into the shoulder of Italian defender Giorgio Chiellini just 14 months after he had to apologise for doing the same thing in Britain.
Suárez could now be banned by world football's governing body for up to 24 matches or two years if he is found to have breached disciplinary rules.
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Down they go: Both men fell to the ground, with Chiellini clutching his shoulder and Suarez holding his teeth
Did he or didn't he? Close-up images showed the moment Suarez leaned in onto his opponent's shoulder
The clash last night in the sweltering Arena das Dunas in Natal, Brazil, came in the final 15 minutes of a tense decisive match between Italy and Uruguay.
Both teams were fighting for qualification for the next round and the score still stood at 0-0 in the final minutes.
Then, Suárez clashed with Italy's Chiellini, with live footage showing him lean his head towards his opponent's shoulder.
Both players fell to the ground with Suárez clutching his infamous teeth while Chiellini gesticulated furiously and pulled down his shirt to show the point of impact.
Close-up images appeared to show the imprints of at least five teeth on Chiellini's naked shoulder.
Opponent: Italy's Giorgio Chiellini looked outraged and showed the apparent point of impact on his shoulder
Evidence: Close-up images showed what looked like the imprints of at least five teeth on his shoulder
FIFA announced it will investigate. A spokesman said: 'We are awaiting the official match reports and will gather all the necessary elements in order to evaluate the matter.'
But Liverpool FC star Suárez was not handed a yellow or red card - and minutes after the confrontation Uruguay went 1-0 up, winning the match and qualifying for the knockout stages.
Chiellini, who plays for Italian team Juventus, reacted furiously after the final whistle and insisted he had been bitten.
He told Rai TV: 'It was ridiculous not to send Suarez off... It is clear, clear-cut and then there was the obvious dive afterwards because he knew very well that he did something that he shouldn’t have done.'
He continued, telling Sky Sports Italia: 'Suarez is a sneak and he gets away with it because FIFA want their stars to play in the World Cup.
Confrontation: Both players fell to the ground with Suarez clutching at his now infamous teeth in pain
'I'd love to see if they have the courage to use video evidence against him. The referee saw the bite mark too, but he did nothing about it.'
The fierce clash came as the Arena das Dunas sizzled in temperatures of 33C and bright sunshine this evening.
Within minutes #Suarez was Britain's quickest-trending phrase on Twitter as fans reacted with a collective groan.
'It is clear, clear-cut and then there was the obvious dive afterwards because he knew very well that he did something that he shouldn’t have done'
Italy's Giorgio Chiellini
Instantly there were memes of the outspoken player concealed behind a dogs' veterinary collar, vampire fangs and a Hannibal Lecter-style mask.
Broadcaster and Mail on Sunday columnist Piers Morgan tweeted: 'Does Suarez not eat before games?'
BBC radio commentator Conor McNamara claimed journalists from Uruguay were laughing and making pretend bite gestures in the stadium. But English pundits were less impressed. Former England winger Chris Waddle said on BBC Radio 5 Live: ‘Luis Suarez has to be severely punished.’
Pundit and ex-England player Danny Mills said: ‘Three strikes you have to be out. Biting someone at a tournament of this prestige, they have to throw the book at him and lock him up forever.’
Thousands of disgusted Twitter users called for Suarez to be banned from football. Former England defender Rio Ferdinand said: ‘Tell me Suarez didn’t eat someone. He was the hero a couple of days ago.’
Others asked if he thought he was ‘playing for Hungary’.
Any action would depend on FIFA judging the case using video evidence, which its President Sepp Blatter is on record this year as supporting.
For now, the future of Suárez at the World Cup depends on the report of Mexican referee Marco Rodriguez, who appeared not to have seen or realized the severity of the incident.
There was anger at the apparent omission from Italy fans, as their team had already been down to 10 men after midfielder Claudio Marchisio was handed a red card in the 59th minute.
Lightning strikes twice: Twitter reacted with appropriate amusement and bemusement, including Piers Morgan
Meme: A betting firm took advantage of the furore using a Photoshopped Hannibal Lecter-style mask
Film references: Instantly memes were comparing the Uruguayan player to the shark from Jaws and a vampire
Just 14 months ago Suárez spent 10 matched on the benches and apologised for biting Chelsea defender Branislav Ivanovic in a 2-2 draw between Liverpool and Chelsea.
'I am deeply sorry for my inexcusable behaviour earlier today during our match against Chelsea,' he said at the time.
WORLD CUP RECORD BANS
If Suárez is found guilty he could be facing the longest ban in World Cup history.
At a maximum of 24 matches, it could far outstrip the eight-match ban handed to Italy's Mauro Tassotti for breaking Spain's Luis Enrique's nose in 1994 with an elbow.
Zinedine Zidane of France was also given a three-match ban for headbutting Marco Materazzi of Italy in the 2006 final.
Suarez has twice been banned for biting opponents. The first time was in 2010, when he was given a seven-game ban while playing for Ajax for biting PSV Eindhoven's Otman Bakkal.
Italy needed only a draw to advance through to the knock-out stages in last night's match, while Uruguay needed a win to reach the last 16.
Both sides had chances from free kicks early on.
Italy goalkeeper Gianluigi Buffon punched away the danger following an effort from Suárez after seven minutes, while Uruguay counterpart Fernando Muslera tipped over a shot directly on goal from Andrea Pirlo in the 12th.
Italy controlled much of the half with its passing accuracy in midfield while Uruguay relied on swift counterattacks and even attempted to surprise Buffon with shots from its own half.
Suarez also had an angled effort smothered by Buffon in the 33rd and a rebound effort from Nicolas Lodeiro was also stopped by the Italy captain.
HE'S GOT HISTORY: THE MANY CONTROVERSIES OF LUIS SUÁREZ
Suárez apologised, received a 10-match ban and was offered anger management classes in April last year after the Uruguayan bit an opponent in front of millions of television viewers around the world.
The Professional Footballers' Association (PFA) said the controversial Liverpool striker, 26, should have counselling after he sank his teeth into the arm of Chelsea defender Branislav Ivanovic during their 2-2 draw.
Suárez apologised, saying: 'I am deeply sorry for my inexcusable behaviour earlier today during our match against Chelsea.
'I have issued an apology and have tried to contact Branislav Ivanovic to speak to him personally. I apologise also to my manager, playing colleagues and everyone at Liverpool Football Club for letting them down.'
He also took to his Twitter profile to say sorry to the Chelsea defender, posting: 'I'm sad for what happened this afternoon, I apologize Ivanovic and all football world for my inexcusable behaviour. I'm so sorry about it!!'
He later added: 'I've just spoken to Ivanovic on the phone and I could apologise directly to him. Thanks for accepting.'
But Suárez had been in trouble for biting players before.
He earned the nickname 'The Cannibal of Ajax' and a seven-match ban in 2010 for drawing blood from the shoulder of PSV Eindhoven's Otman Bakkal while playing in Holland.
And in 2011, Suarez received an eight-match ban and was fined for racially abusing French defender Patrice Evra in a match against Manchester United.
The FA found Suárez had called Evra a 'Negro' or 'Negros' seven times during the game - though the player insisted his words had been lost in translation.
In 2010, Suarez was guilty of pulling off one of the World Cup's most glaring fouls when he stopped a goal-bound header from Ghana with his hand late in extra time.
Suarez, who was sent off, hung around near the tunnel to watch Ghana's Asamoah Gyan miss the penalty and then celebrated frantically, enraging neutral fans. Uruguay ultimately won in a shootout to go through to the semifinals.
Suarez later boasted: 'Truth is it was worth it.'
