The defender admitted that the Seleccao are dependent on the Real Madrid forward shaking off his injury woes if they are to reach the latter stages of the World Cup
The 29-year-old scored 51 goals in 47 appearances last season for Real Madrid, helping the Blancos win their 10th Champions League, in addition to the Copa del Rey.
However, Ronaldo has been blighted by injury issues since April and pulled out of training on Thursday after issues with his left knee, casting doubt on whether he will be in top shape for the Seleccao's opening clash with Germany on Monday.
Bruno Alves, a veteran in defence for Paulo Bento's men, acknowledged that Portugal would be a much weaker team without the two-time Ballon d'Or winner.
"The greatest player in world football had to be present at the World Cup and he will help the team achieve our aims," the Fenerbahce man, 32, told Antena 1. "We rely on our captain Ronaldo, always.
"The rest of the squad are all competing for a place in the starting line-up and we are all motivated. We've arrived in Brazil in good shape for the World Cup.
"All of the games will be difficult but we're keen to start well against Germany. Portugal have quality players who can make a difference in the World Cup - anything can happen. We can't make any predictions, but we all have dreams and goals."
Portugal follow Monday's 18:00CET clash with Germany with a tie against USA on June 22 before facing Ghana in their final group stage match on June 26.
They will be hoping to better their second round exit in 2010 and trying to at least match their World Cup 2006 showing - when they reached the semi-finals.