Uruguay star Luis Suarez faces expulsion from the World Cup for biting another player as Fifa confirmed it had opened disciplinary proceedings against him on Wednesday.
Suarez, banned twice before for biting opponents, appeared to sink his teeth into defender Giorgio Chiellini on Tuesday during Uruguay's 1-0 win over Italy.
Uruguayan players and team officials pleaded ignorance but the incident was captured clearly on television footage, making a ban almost inevitable.
Watch: Biting incident mars Uruguay World Cup win
"Fifa can confirm disciplinary proceedings have been opened against the player Luis Suarez," Fifa said in a statement.
Suarez and the Uruguayan Football Association can submit evidence to investigators until 5:00pm (2100 GMT) on Thursday, FIFA added.
Suarez, who plays in the English Premier League for Liverpool, is one of the world's biggest stars, and could be banned for up to 24 games under FIFA rules.
He has already received long bans for biting during his club career as well as racially abusing Manchester United player Patrice Evra during a game in 2011.
The latest flashpoint in his occurred towards the end of Uruguay's Group D game with Italy.
Replays showed Suarez appearing to bite Chiellini's shoulder as the two players made contact in an off-the-ball incident.
Chiellini angrily remonstrated with Mexican referee Marco Rodriguez, pulling his shirt off his shoulder to show red marks on his neck.
Afterwards a disgusted Chiellini told Italian television: "He bit me, it's clear, I still have the mark."
"The referee should have blown his whistle and given him a red card," he added.
"There are things that happen on the pitch and you should not make such a big deal out of them," Suarez said.
Bite marks? pic.twitter.com/lFHFpRaazq— Gary Lineker (@GaryLineker) June 24, 2014
Tabarez 'didn't see' bite
Uruguay's veteran manager Oscar Tabarez pleaded ignorance of the incident.
"I didn't see it. I'd like to see the images first," he told a press conference.
Tabarez also suggested Suarez was being victimised by journalists. "He is the preferred target for a lot of media," Tabarez said.
Pressed on the issue, a visibly irritated Tabarez refused to condemn Suarez. "This is a football World Cup, it's not about cheap morality."
But senior Fifa officials wasted no time in condemning the striker.
"There is no doubt Luis Suarez is a fantastic footballer but once again his actions have left him open to severe criticism," FIFA vice-president Jim Boyce told the BBC. "Fifa must investigate this incident very seriously and take whatever action is deemed necessary."
If found guilty, the incident means the end of the tournament for Suarez, lambasted during the 2010 World Cup for his goal-line handball which denied Ghana what would have been a quarter-final victory.
In November 2010 he was banned for seven matches by the Netherlands FA after biting PSV Eindhoven's Otman Bakkal on the shoulder when he played for Ajax.
Suarez was dubbed "the Cannibal of Ajax" by Dutch media.
In 2013, he was given a 10-match ban by the English FA after biting Chelsea defender Branislav Ivanovic in a match at Anfield while playing for Liverpool.
"This is behaviour that's happened two times (before). You cannot justify it. I seriously think he needs help," said Everton manager Roberto Martinez after the latest Suarez transgression.
English former World Cup referee Graham Poll said Suarez should be banned from the tournament.
"Luis Suarez should not be allowed to kick another ball in this World Cup," Poll wrote in a column for the Daily Mail.
The biting storm dominated the headlines on Tuesday after Uruguay downed Italy 1-0 to advance to the last 16.
Luis Suárez enjoying his post-match meal... pic.twitter.com/JBxgy2JA5e— Footy Laughs (@FootyLaughs) June 24, 2014
Suarez will have to wear this for the rest of the tournament pic.twitter.com/T1rYzTgNTa— Josh Gigante (@JoshGigante_) June 24, 2014
FIFA technology says... pic.twitter.com/zinAvKqJtW— Football Funnys (@FootballFunnys) June 24, 2014
In the other Group D game, Costa Rica ensured England's miserable World Cup ended with a whimper in a 0-0 draw.
The result meant Costa Rica win the group, unbeaten after three games, with Uruguay finishing as runners-up.
Costa Rica will play Group C runners-up Greece on Saturday after they scored a last-gasp 2-1 win over Ivory Coast to scrape into the last 16.
An injury time penalty from Georgios Samaras clinched victory for the Greeks and left Ivory Coast players shattered.
Colombia wrapped up qualification for the last 16 with another impressive win, destroying Japan 4-1 in Cuiaba.
Colombia will now face Uruguay, almost certain to be without Suarez.