Ronaldo trained on Sunday, easing concerns over his fitness ahead of Portugal's FIFA World Cup campaign.
Vieirinha was delighted to see the Real Madrid star back as Bento's side prepare for a friendly against the Republic of Ireland on Tuesday.
"For us it is important to know how important Cristiano Ronaldo is," the midfielder said.
"His presence on the national team, gives motivation to the other players. It is very important to us and very important to Portugal, because he is another player who will help the team."
Portugal have struggled without Ronaldo in their pre-tournament friendlies, held to a 0-0 draw by Greece before needing a late goal to edge Mexico 1-0.
Vieirinha said Ronaldo's return was 'the best thing that could have happened', and also said he had a role to play.
"I feel able to help the team. If I couldn't do it, probably I wouldn't be here, for sure," the Wolfsburg man said.
"About Cristiano Ronaldo, I think the last training answered the questions that everyone had. I think this training shows he came to help the team and all of us are happy with it.
"We hope this stays in this way, without creating a lot of expectations with him being back in the team.
"I believe that was the best thing that could have happened in recent days."