When chasing a ball in the second half, the Real Madrid defender pulled up clutching his adductor, and had to be stretchered from the field, holding his face in pain.
And after an assessment by the Portugal medical staff after the match that ruled him out for the rest of the group stage, Coentrao revealed that his worst fears were all but realised.
"I honestly think the World Cup is over for me," he lamented to AS.
"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,"
Forward Hugo Almeida was also forced from the pitch, and Portugal’s head of medical services Henrique Jones confirmed that both players would be unavailable for "between 10 days and three weeks".
The prognosis rules the pair out of Portugal’s remaining group games against Ghana and USA, which will effectively end their participation in the World Cup should the Seleccao fail to qualify.