Cristiano Ronaldo's fitness ahead of Portugal's World Cup opener against Ghana remains a worry for coach Fernando Santos.

The Manchester United forward missed the final warm up game against Nigeria at the José Alvalade Stadium due to illness.

Before the friendly against Nigeria, he had missed training and it is yet to be known if he will be fit in time for the game against Ghana.

“Ronaldo has gastritis and did not train today in order to recover and rest," said Santos.

Ronaldo's absence will be a huge blow for the 2016 European champions as they eye a good start to their World Cup campaign. He scored the winner when Ghana face Portugal at the 2014 World Cup.

The tournament is expected to be the five-time Ballon D'or winner's last dance at the international stage.

Portugal will play Uruguay four days after their opener against Ghana before engaging South Korea in their final group game.