Cristiano Ronaldo is in danger of missing at least Portugal's opening match at next year's World Cup after being showing a red card in Thursday's 2-0 loss to the Republic of Ireland.

Ronaldo was initially shown a yellow card after elbowing Ireland defender Dara O'Shea during the match in Dublin. However, it was upgraded to a red card and Ronaldo was sent off for the first time in his international career after the contact was reviewed by the referee on a pitch-side video monitor.

"When he tries to get away from the defender, I think the action looks worse than what it actually is," Portugal coach Roberto Martinez said. "I don't think it's an elbow, I think it's a full body. But from where the camera is, it looks like an elbow. We accept it. It could be a red card but for the right reasons."

Ronaldo will serve his mandatory one-game suspension when Portugal plays host to Armenia on Sunday. Portugal, which still lead Hungary by two points in Group F, can clinch a spot in next year's World Cup with a victory.

However, FIFA disciplinary rules state that a ban of at least two matches is required for "serious foul play" and for at least three matches for "violent conduct," or for "an appropriate period of time for assault, including elbowing."

Pre-World Cup exhibitions would not count towards serving a potential match ban, and it could be three weeks before FIFA issues a verdict.

It is the first red card Ronaldo has received in the record 226 games he has played for Portugal.

"He is just a captain that has never been sent off before in 226 games," Martinez said. "I think it was a bit harsh because he cares about the team."

Ronaldo is seeking to reach his sixth World Cup.