International football officials met on Wednesday to decide whether Uruguay striker Luis Suarez should be punished -- possibly thrown out of the World Cup -- for biting an opponent.
A disciplinary panel gathered evidence against Suarez, who shocked football when he was shown sinking his teeth into Italy's Giorgio Chiellini.
As Suarez, banned twice before for biting opposing players, awaited the outcome of the disciplinary hearing, Uruguay's President Jose Mujica rallied his country to the footballer's cause.
"I did not see him bite anyone," Mujica told reporters. "But they give each other so many kicks and blows and normally they put up with it."
Uruguay Football Association chief Wilmar Valdez presented evidence on Suarez's behalf to a FIFA panel in Rio.
"We believe that there is not sufficient evidence to truly sanction Luis," Valdez told Uruguay's Channel 10 television.
"It has to be clear and on the video that FIFA gave us we think that it is not really clear," Valdez said.
"We are confident that our defence will obtain results," he added.
FIFA spokeswoman Delia Fischer said earlier the disciplinary committee wanted to reach a decision on Suarez's case "as early as possible."
Uruguay are due to face Colombia in the last 16 on Saturday.
Fischer would not speculate on any possible punishment, although she said Suarez's previous offences could be taken into account.
"The disciplinary committee can take all elements into account as it deems necessary," she said.
Suarez was nowhere to be seen Wednesday as his Uruguay team-mates trained in Natal amid the raging controversy.
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The 27-year-old, who plays in the English Premier League for Liverpool, is one of the world's biggest stars, and could theoretically be banned for up to 24 games under FIFA rules.
Fischer declined to say whether any potential punishment could extend to club as well as international football.
"It's the disciplinary committee which decides the scope of any potential sanctions," she said. (FIFA tight-lipped on possible Suarez sanctions)
Suarez 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 occurred near the end of Tuesday's Group D game in Natal.
Replays showed Suarez biting Chiellini's shoulder 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, he told Italian television: "He bit me, it's clear, I still have the mark."
Suarez sought to play down the incident in comments to Uruguayan television, claiming Chiellini had barged him.
- 'Suarez needs help' -
However the damning video evidence has drawn almost blanket condemnation.
Former England captain Alan Shearer, working in Brazil for the BBC, said FIFA should impose a lengthy global ban.
"I would give him a worldwide ban for as long as I could," Shearer said.
"It's not the first time, it's not the second time, it's the third time -- to actually bite someone on a football pitch in front of millions. It's unacceptable."
Sponsors warily watched the FIFA inquiry.
Online gambling firm 888poker said it was "reviewing" it's relationship with the player. "We will not tolerate unsporting behaviour," the enterprise said.
German sporting goods manufacturer Adidas said it was awaiting FIFA's "full investigation into this matter."
Many in Uruguay believe that Suarez is being unfairly persecuted.
Suarez's Facebook profile rapidly filled with dozens of messages in English and Italian branding him a "cannibal," prompting other users to rally behind him.
"Be strong Luis. It's clear they're persecuting you," said user Sandra.
"There is no doubt that Suarez is a stone in the shoe for many," said Alejandro Balbi, a lawyer for Suarez who serves on the Uruguay FA.
An exception was ageing national hero Alcides Ghiggia, who scored Uruguay's World Cup-winning goal against Brazil in the 1950 tournament.
"This boy's clearly not right in the head. That's just not something you do on the pitch,' said Ghiggia.
With the Suarez controversy dominating the off-field headlines, it was left to Argentina captain Lionel Messi to put the focus back on football.
Messi scored two goals -- taking his tournament tally to four in three games -- as Argentina beat Nigeria 3-2 to finish top of Group F.
Nigeria also reached the last 16 for the first time since 1998 despite the defeat after Iran were beaten 3-1 by already eliminated Bosnia.
In the late games France and Switzerland both sealed qualification from Group E. France topped the group after a 0-0 draw with Ecuador while Switzerland beat Honduras 3-0.