The Paris Saint-Germain stopper, fresh from the Selecao's 6-0 friendly win against Australia on Saturday, had hoped to come up against the 28-year-old following his devastating hat-trick against Northern Ireland on Friday but has been ruled out because of tendinitis.
"Portugal are a very strong team, they've been playing tough international challenges for some time now. I watched the goals yesterday, the three from Cristiano," Silva told reporters.
"Someone said he's not playing, that he felt something, but who knows? It could be one of those little lies. But regardless of that, their team is really strong. We need to be ready to face them.
"I'm not happy that he [Cristiano] is out. It's always a sad thing to see a fellow footballer getting injured. We had that today with Marcelo. A player of Cristiano's calibre should always be fit to play, because that makes any match automatically better."
Chelsea star Oscar also expressed his sadness that the Real Madrid will not be able to play. "It's a pity that Cristiano Ronaldo won't be there," he said.
"Portugal have a great team; it's not just him. They have other good players. It will be a tough challenge."
David Luiz, who partnered Silva at the back on Saturday believes Ronaldo's absence gives Brazil impetus.
He told reporters: "When one of the best players in the world isn't fit to play, it's always better for who's playing against his team."
Brazil bounced back from the Switzerland defeat with an emphatic victory over the Socceroos, with goals coming from Jo, Neymar, Ramires, Alexandre Pato and Luiz Gustavo.
Silva will expect to be tested far more in Tuesday's friendly than he was on Saturday but insisted that credit must be given to the way Luiz Felipe Scolari's men defended as well as attacked.
"We didn't have a difficult life today because of how well our defence worked, it's important to highlight that," he continued.
"Let's not say that they didn't make it past our back line because of their lack of quality, but because we did a very good job at keeping them from it. We had a really strong man-marking [system]."
