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Coentrao, who was deployed in a midfield role for the match, made signals to be taken off on 62 minutes and was seen clutching his adductor, clearly in a lot of pain.
Afterwards Coentrao was not hopeful that he would be able to return in time to play any further part in Portugal's World Cup campaign.
He said: "I honestly think the World Cup is over for me. I'm sure it's a serious injury although I hope I'm wrong.
"Sadly, these things happen in this job. It's a sad day, one of the saddest of my life but it's only the first game and despite the result, we could still get through to the next round."
He and fellow casualty Hugo Almeida will undergo tests on Tuesday and again on Wednesday to determine the extent of their injuries.
Head of medical services for the Portugal national side Henrique Jones estimates that both players will be out for "between 10 days and three weeks" which mean neither will be available for the next group stage games against United States and Ghana.
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