Uruguay's Luis Suarez faces a lengthy ban that would force him to miss the rest of the World Cup if found guilty of biting Italy's Giorgio Chiellini.
Fifa, football's governing body, has opened disciplinary proceedings against the striker following Uruguay's 1-0 group win on Tuesday.
Chiellini claimed Suarez bit him on the left shoulder, but Suarez said the defender "bumped" into him.
Chiellini pulled down his shirt to display what appeared to be bite marks on his shoulder
Suarez, 27, could be banned for up to 24 matches or two years.
Mexican referee Marco Rodriguez took no action following the incident, but Fifa can still punish Suarez.
Radio 5 live's Richard Conway, who is in Brazil to report on the World Cup, said: "Fifa will want to deal with this quickly so attention can once again return to matters on the pitch.
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Match of the Day pundits react to the 'bite'
"Given that spitting at an opponent carries a minimum tariff of six games, you would expect biting to carry a ban in excess of that.
"That gives you the benchmark many people are working on and would mean his World Cup would be over."
Former Liverpool midfielder Jan Molby expects Suarez to be banned for the rest of tournament.
The Dane told the
Liverpool Echo newspaper: "I'm sure Fifa will make an example out of him. Obviously, his World Cup is over and I would expect Fifa to give him a long international ban."
The longest ban in World Cup history is eight games, handed out in 1994 to Italy defender Mauro Tassotti for breaking Spain's Luis Enrique's nose with his elbow during the second half of their quarter-final.
Uruguay face Colombia in the last 16 on Saturday after finishing second in Group D behind Costa Rica.
Suarez and the Uruguayan Football Association have until 21:00 BST on Wednesday to respond to Fifa.
“Suarez should never play international football again”
Robbie SavageBBC pundit & former Wales midfielder
Former England captain Alan Shearer told BBC Sport: "The pictures are damning and I don't see how he can get away with it."
Chris Waddle, a member of England's World Cup squads in 1986 and 1990, said: "There will be people who will defend him, but I don't know why. I'd make him wear a gumshield."
Suarez has twice been suspended for biting opponents.
In December 2011, Suarez was also given an eight-match suspension and fined £40,000 for racially abusing Manchester United's Patrice Evra.
After the Ivanovic incident, Liverpool said they had spoken to Suarez about his "unacceptable" behaviour.
Luis Suarez's controversies
July 2010: Handles the ball on the line to deny Ghana a winner in the last minute of extra time in the World Cup quarter-finals. Asamoah Gyan misses the resulting penalty and Uruguay win the shootout to reach the semi-finals.
November 2010: Given seven-match ban for biting PSV Eindhoven's Otman Bakkal on the shoulder while playing for Ajax.
December 2011: Given eight-match suspension and fined £40,000 for racially abusing Manchester United's Patrice Evra.
February 2012: Refuses to shake hands with Evra at Old Trafford and is described as a "disgrace" by United manager Sir Alex Ferguson.
April 2013 : Suarez apologises for biting Chelsea defender Branislav Ivanovic. Gets 10-game ban.
"This is a club with incredible values and ethics," said Reds boss Brendan Rodgers at the time. "There's certainly no-one bigger than this club, a player or manager."
Suarez has also been criticised during his career for diving and stamping during games, prompting former Liverpool director of football Damien Comolli to suggest the Uruguayan could be driven out of England.
"This is a person who definitely needs some help," former England boss Graham Taylor told Radio 5 live.
"If you look at Suarez's reaction afterwards, it's like he knows what he's done."
Last season, he helped Liverpool to a second-placed finish in the Premier League, winning the Golden Boot with 31 goals in 33 games.
He was named player of the year by both the Football Writers' Association and Professional Footballers' Association.
Liverpool have not made any comment on the latest incident and will let Fifa deal with it before deciding on any action.
Asked about the alleged bite, Suarez told Uruguayan television after the game: "There are things that happen on the pitch and you should not make such a big deal out of them. It was just the two of us inside the area and he bumped into me with his shoulder."
Chiellini, 29, described Suarez as "a sneak".
He added: "I'd love to see if Fifa has the courage to use video evidence against him. The referee saw the bite mark but he did nothing about it."
The referee took no action at the time of the incident
Fifa vice-president Jim Boyce said: "There is no doubt Luis Suarez is a fantastic footballer but, once again, his actions have left him open to severe criticism.
"Fifa must investigate the incident seriously and take whatever disciplinary action is deemed necessary."
After the clash between the players, Suarez fell to the ground holding his mouth, apparently suggesting he had been elbowed.
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Suarez's controversial career
Chiellini ran after the referee to show him the alleged bite mark, pulling his shirt down to bare his left shoulder.
As he did so, Uruguay forward Gaston Ramirez tried to stop him by pulling the Italian's jersey back into place.
The incident occurred towards the end of the game, shortly before Suarez's team-mate Diego Godin scored the only goal of the match.
Godin's header eliminated four-time champions Italy from the 2014 Fifa World Cup and secured Uruguay, semi-finalists in South Africa four years ago, a match against Colombia in the next round.