When Ronaldo was suspended, the Portuguese cruised past Armenia in last month's final World Cup qualifier, 9-1, to seal a place in next year's big event.
"Cristiano inside the box continues to be a very high-level player," Fernandes, the captain of Manchester United, said in an interview with Canal 11.
"He draws defenders and creates space for other players. If Cristiano doesn't play and [Paris Saint-Germain's] Gonçalo [Ramos] does, Gonçalo is strong in pressing and good at diagonal runs.
"When I'm not playing and Bernardo [Silva] is playing as a number 10, Bernardo gives you more possession, I make more of a final pass. It's all like that. All players add things and take away others. Cristiano is the same as us. We have to know how to adapt and enhance each other's qualities so that the national team benefits."
Ronaldo, 40, is the all-time men's international goalscorer with 143 goals in 226 appearances for Portugal since making his debut in 2003.
His time with the national team looked to be in jeopardy when he was benched by Fernando Santos during the 2022 World Cup.
However, his goalscoring form with Saudi Pro-League outfit Al Nassr has allowed Ronaldo to return to Portugal's starting XI under Santos' successor, Roberto Martinez.
"I know what people think, that it's clear we play better without Ronaldo, that the players are freer and more fluid," Fernandes said. "I think that, if that happens, it's partly our fault. We can't worry if Cristiano is on the pitch, because Cristiano can give us things."
Portugal, who beat Euro 2024 winners Spain to win the UEFA Nations League title in the summer, have high expectations heading into the 2026 World Cup.
They qualified with four wins and just one defeat while scoring 20 goals, five netted by their leading scorer Ronaldo, and conceding seven in six games.
"I want to play in the 2026 World Cup, but if I have to be on the bench for us to be champions, I'll sign for that twice," Fernandes said.
- Bruno Fernandes: I want to play in Spain or Italy after Man United
- Fernandes: Man United 'wanted me to go' after summer Saudi offer
- Fernandes' hurt feelings show he's missing the bigger picture at Man United
Fernandes, 31, has high expectations heading into his third World Cup.
It will also represent Ronaldo's last opportunity to lift the only major trophy missing in his distinguished career.
"We dream of winning the World Cup and that responsibility is positive," Fernandes said. "We must close ranks as a group and figure out where to improve, and understand that the World Cup won't be perfect. I know we are prepared to have a great campaign that will bring honor to the country."
