In an interview with Barca TV and www.fcbarcelona.cat, Belletti also claimed that the Spanish giants were not "unstoppable".
Belletti is unlikely to start against his former club in the fist-leg in the Nou Camp on Tuesday but says the tie is "worthy of the final".
"I think the winners will end up being champions," said Belletti. "Barca have beaten some of the great teams of Europe, and we've beaten Juventus and Liverpool. So whoever picks up the cup will have defeated the best in Europe.
"I think people thought this would be the final. Obviously there are other great teams like Liverpool and Manchester United, but Barca and Chelsea are the two best teams in their leagues at the moment. It's a game worthy of the final.
"Nobody is unstoppable. I've played in the Brazilian national side for a long time and we've never thought we were unstoppable. When I was with Barca we played great football but we weren't either. Unstoppable teams don't exist.
"They play at a high level both on and off the ball. In my Barca days, I remember we put on the pressure when we lost the ball. They still do this now and the Chelsea players are aware of it.
"But I've never been with a team like Chelsea, a team that wants to win more. Some of the players have won just about everything, but they never give up fighting.
"We have some great individual players, but we are also a great team. Didier Drogba, Frank Lampard and John Terry are on great form, and Nicolas Anelka is regaining his form.
"What makes us a strong side is our desire to win the Champions League. Our weaknesses depend on the day. We're capable of going to Camp Nou and not losing.
"I think the second leg will be decisive. In the first leg you still know you have another 90 minutes. It would be great to score in Nou Camp, but we also realise we can't afford to let any goals in. We want the semi-final to be decided at home."
The Chelsea defender believes the game will be decided by a slice of individual genius and there are plenty of players on both sides capable of providing it.
"I think Barca's game is very different from Chelsea's," added Belletti.
"The English just want to score goals, play attacking football, whereas Barca have always played possession football, players working alongside each other.
"In games like these, individual moves can be decisive. Barca have Lionel Messi, Thierry Henry or Samuel Eto'o. Chelsea have Drogba, Anelka and Florent Malouda, who is on great form.
"We are very good from free kicks or in the air. But in games like these, individual moves normally decide the result."