Cristiano Ronaldo returns to face former club Manchester United tonight with club Juventus.
Meanwhile, Carlo Ancelotti managed Ronaldo at Real Madrid where together they won the Champions League, Copa del Rey, Super Cup and Club World Cup.
The Italian is now Coach at Napoli, who are demanded to win the Italian Serie A.
However, Ancelotti has revealed one mistake Ronaldo made his football career.
“The only failure of Cristiano has been signing for Juventus,” he joked.
"The arrival of Cristiano is an excellent sign for the image of Serie A,” Ancelotti told France Football.
“For a long time it was the championship of the stars: Maradona, Platini, Zico, Zidane, Ronaldo, Shevchenko, Kaka, Ibra… but in the last ten years."
Napoli are currently just four points behind Juventus in the Serie A table.
Massimiliano Allegri's team failed to win over the weekend and drew 1-1 against Genoa.
Juventus have already beaten title rivals Napoli 3-1 back at the end of September.
"Now it's a different club, we do not have [Diego] Maradona,” Ancelotti added.
“We have a high level team that was built mainly with young players, the team has played well in recent years, the quality is there, I will try to contribute experience and help the team to have more personality.”