Cape Town - Vieirinha is convinced Cristiano Ronaldo will have shrugged off his recent injury in time for Portugal's opening match at the 2014 World Cup.
The Real Madrid superstar has missed his country's last two friendly matches with tendinosis in this left knee, raising fears the Ballon d'Or holder may miss the Brazil showpiece entirely.
However, Ronaldo returned to light training on Sunday and could feature in Portugal's final warm-up match, against Republic of Ireland on Wednesday, according to Wolfsburg midfielder Vieirinha.
The playmaker said of Ronaldo: "If he is fit to train, he is fit to play the match."
"Everybody knows the importance of Ronaldo to our team and his importance to the group, both on and off the pitch."
Portugal find themselves in the World Cup's 'Group of Death', having been drawn against Germany, Ghana and the United States, with their opener coming against the Germans on Monday, June 16.
Looking ahead to their opener, Vierinha added: "We all know that the first game is always the most important.
"We know how good the Germans are, but we also know what we can do against them. There are a lot of good teams at the World Cup.
"But we just need to do our work and what we do on the pitch is our responsibility, nobody else's.
"Our first goal is to get through the group stage, and if we do that, we'll see how far we can go."