The Barcelona midfielder was dismissed for striking Mario Mandzukic off the ball as Cameroon crashed out of the tournament following a 4-0 loss to Croatia on Wednesday
The Barcelona man was sent off for elbowing striker Mario Mandzukic in the back as Volker Finke's men slipped to a second defeat at the World Cup, going down 4-0 in Manuas.
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"I'm very sad at the moment as I feel I have let my country and myself down," he said in a statement.
"It was a stupid moment and I'm truly sorry. If I could do anything to take it back I would. Please forgive me."
Cameroon are now out of the competition and also saw Benoit Assou-Ekotto involved in an unsavoury tangle with team-mate Benjamin Moukandjo late on, an incident coach Volker Finke described as "unimaginable".
"I saw this happen and I need to find out exactly what happened, why exactly these two players exploded. I hate to see that. It's not the image of Cameroon I want to project."
Cameroon will seek to restore some pride when they face hosts Brazil in the final game of their campaign.