The former Brazil international feels it is too soon to write off the Blaugrana, and expects a tight Champions League encounter between Manchester United and Real MadridBarcelona's era is over and believes they remain the best team in the world.
The Catalans were beaten 2-0 by AC Milan in the first leg of their Champions League round of 16 tie, and have also been eliminated from the Copa del Rey and defeated in La Liga by arch-rivals Real Madrid over the past few weeks.
But Carlos told AS: "Barcelona are still the best team in Europe. Despite the absence of their head coach, they remain a very strong team. You cannot dismiss them after just three losses.
"I believe that they can turn things around against Milan. The problem with Barcelona is that they have been playing together for a long time and suffer from mental fatigue.
"Nevertheless, they remain a force to be reckoned with and I hope that they will recover."
The former Brazil international also had his say on Real Madrid's Champions League match versus Manchester United on Tuesday, and expects a tight encounter at Old Trafford.
"Madrid can put in a good performance as they are high on confidence. It will be very difficult as it's an away game, but they can make it happen.
"It will be an even tougher game than the two matches versus Barcelona. United are very well organised and remain focused for the full 90 minutes. Manchester have a dangerous team."
Madrid were held to a 1-1 draw in the first leg at the Santiago Bernabeu.