Juventus face a Barca side still reeling from last Saturday's shock 2-1 defeat to newly-promoted Cadiz in LaLiga which left them 12 points behind leaders Atletico Madrid after 10 games.
Ronald Koeman's side have, however, been flawless in the Champions League with five victories from five Group G matches, including a 2-0 win in Turin in October.
Juve's only win at Camp Nou in the Champions League came back in April 2003 (2-1), having failed to win on either of their last two trips there in the competition.
The Bianconeri have not scored in their last four games against Barca and Pirlo said they are not on the verge of meltdown, despite a domestic blip.
"I don't believe in the Barcelona crisis," Pirlo told a media conference. "The club has a new coach who is putting his ideas together. We know that he has a great team.
"They changed coaches but always go out on the pitch to play. They have to find the best solutions and put the players in the best conditions to perform at their best.
"But you play every three days and it's difficult for them, too. They are a great team and they will also recover in the league."
🎙 @Pirlo_official: "@RonaldKoeman is right: it would be wrong to say who is better between Messi and @Cristiano. They are two phenomenons that put on spectacles for millions of fans. We just have to thank them."#BarçaJuve #JuveUCL— JuventusFC (@juventusfcen) December 7, 2020
Messi and Ronaldo have previously met in five Champions League encounters, with Messi 3-0 up on the Portuguese superstar in terms of goals.
Tuesday's fixture will be their first duel in the competition since the May 2011 semi-final between Barcelona and Real Madrid and the first for Ronaldo as a Juve player.
On the eve of the match Barcelona head coach Koeman diplomatically refused to rank Messi as a superior player to Ronaldo, and his Juventus counterpart followed suit.
"Koeman is right to say that it is not fair to say who is better," Pirlo explained. "They have put on a show and have been doing it for 15 years. They have shared the Ballon d'Ors of the last 15 years.
"It is a shame to say if one is better than the other. They are phenomena that make millions of fans rejoice every time they take to the pitch, it is not fair to say who is better.
"We must thank them both because they are good for football.
"Messi had some problems this summer in wanting to stay in Barcelona. But in matches he has always proved his worth so more than on a technical level I think it's a mental problem.
"We don't want to get into problems, however, so let's leave Barcelona and Messi talking about these things."
Pirlo hinted veteran goalkeeper Gianluigi Buffon is in line to feature against Barca, having returned to training following a thigh problem.
He said: "Gigi is better. He has recovered from his injury. He could be in the game tomorrow because he deserves such an important stage and could play."