Ronaldo came into the tournament with a knee problem and played the full 90 minutes in Portugal's opening game against Germany which they lost 0-4.
On Wednesday (June 18), Ronaldo had to cut short his training session with team-mates and his left knee was strapped with ice. A few days before the tournament opener, Ronaldo had to leave the training session due to same problem.
Following his withdrawal from training, rumours surfaced in Brazil that the Real Madrid star will not take any part in the rest of the tournament. However, there is still no confirmation from the team.
Sports writer Ewan MacKenna on Wednesday tweeted that he had heard rumours in press centres at World Cup that Ronaldo is out of the World Cup.
Rumours - unconfirmed may I add - here in press centres in Brazil that Cristiano Ronaldo is out of the World Cup.
Rumours - unconfirmed may I add - here in press centres in Brazil that Cristiano Ronaldo is out of the World Cup.— Ewan MacKenna (@EwanMacKenna) June 18, 2014
His doctor had warned Ronaldo not to play with the knee problem which could jeopardise his future playing career.
Surgeon Jose Carlos Noronha had said to Ronaldo: "Let your knee rest or your future is in danger," according to media reports.
Ronaldo is participating in his third World Cup. He helped Portugal finish fourth in Germany 2006 while in the next edition in South Africa (2010) they went out in the round of 16, losing to eventual champions Spain.
Portugal's next group match is against United States of America on June 22.