What you need to know:
- Messi has won 16 of their 35 encounters to Ronaldo's 10, with the remaining nine ending in draws. Messi has also scored 22 goals in those games to Ronaldo's 19.
- The pair have only met five times in Champions League games, most recently in the semi-final in 2011.
- Barcelona got the better of Real Madrid with a 3-1 aggregate win with Messi scoring twice in the first leg.
Andrea Pirlo sees positives despite preparing for his biggest match since taking over as Juventus coach with Covid-19 -stricken Cristiano Ronaldo in doubt against Lionel Messi's Barcelona in the Champions League on Wednesday.
Pirlo took over after Maurizio Sarri was sacked immediately after Juventus' last 16 exit to Lyon in August, the veteran coach lamenting another failure in a "competition cursed for Juve".
The Turin side have won the tournament twice, but not since 1996. They have been runners-up seven times, including twice in the last five years.
In fact, 41-year-old Pirlo's last Juventus game as a player came in the 3-1 loss to Barcelona in the 2015 Champions League final.
Juventus signed Portuguese star Ronaldo in 2018 with the aim of lifting the coveted European trophy, and his absence against Messi's Barcelona could weigh heavy.
The 35-year-old will need to test negative 24 hours before being allowed to feature in Turin. The return at the Camp Nou is on December 8.
"We miss him right now, of course," said Colombian teammate Juan Cuadrado. "He's a champion. In these very difficult matches, his strength, his mentality and his desire shine through."
Ronaldo scored three goals for Juventus in their first two league games, before contracting the virus while on international duty.
Even if Pirlo has yet to record a loss this season, Juventus are fifth in Serie A, with three draws in five games.
"Barcelona? It doesn't worry me, they are two different matches," said Pirlo after Sunday's 1-1 stalemate against Hellas Verona.
"Verona play differently than Barcelona, against teams that play like this you have to prepare a certain type of match.
"We're in the construction phase," continued the novice coach.
"We're sorry to leave points on the road, but we are on the right path. We are building a long-term project. I only see positive things."
Time running out
Pirlo's main weapons in Ronaldo's absence have been Spanish forward Alvaro Morata, who scored both goals against Dynamo Kiev, and Swedish striker Dejan Kulusevski, who rescued the point against Verona.
Former Chelsea and Real Madrid player Morata returned to Juventus this season with Kulusevski signed from Atalanta in January before being loaned back immediately to Parma.
The 20-year-old Swede was up and running immediately, scoring on his club debut in September and came off the bench to give Juventus the edge against Verona.
Pirlo has also been impressed with how Paulo Dybala performed "well above expectations," in his seasonal debut against Verona after over three months out.
Captain Giorgio Chiellini's presence is in doubt, with fellow defender Leonardo Bonucci's thigh strain being monitored, although Gianluca Frabotta, 21, has stepped into the breach, with Alex Sandro also out.
"Seeing how we started the other championships, this start has been a bit slow," said Cuadrado of the nine-time reigning Italian champions.
"But we haven't lost yet."
Both teams won their Group G openers with Barcelona beating Hungarians Ferencvaros 5-1 and Juventus 2-0 at Dynamo Kiev.
If Ronaldo misses his chance to line out on Wednesday he will have to wait until December to renew his rivalry with Argentine Messi.
They are the two greatest players of their generation with 11 Ballons d'Or between them, and the two highest scorers in Champions League history.
They have not faced off since the Portuguese superstar left Real Madrid for Juventus, and both are running out of time to win the Champions League again.
Messi, now 33, has featured in four victorious campaigns, all with Barcelona, while Ronaldo has won it five times, four with Real Madrid and once with Manchester United.
Ronaldo has 130 Champions league goals, of which ten have been for Juventus, to Messi's 116.
Messi has won 16 of their 35 encounters to Ronaldo's 10, with the remaining nine ending in draws. Messi has also scored 22 goals in those games to Ronaldo's 19.
The pair have only met five times in Champions League games, most recently in the semi-final in 2011.
Barcelona got the better of Real Madrid with a 3-1 aggregate win with Messi scoring twice in the first leg.
Their most memorable clash was the 2009 Champions League final when Messi scored as Barcelona beat Manchester United 2-0.