The Old Lady have named former Italian national team boss Spalletti as their manager until the end of the season.
Spalletti takes over from the Croatian manager, who was dismissed following the loss to Lazio last weekend.
The former boss came on board in March to replace Thiago Motta but left after seven months at the end of an eight-match winless run.
Spalletti led Napoli to the Serie A title in 2022-23 prior to assuming the Italy role, after the team's failure to reach the 2022 World Cup with Mancini at the helm.
He helped them qualify for Euro 2024 where they were knocked out in the last 16 by Switzerland.
Nonetheless, Italy dismissed Spalletti in June post a qualifying defeat against Norway, with the Azzurri at risk of missing out on a third consecutive World Cup.
Spalletti's managerial career includes Inter Milan, Roma, and Udinese in Serie A and won the Russian Premier League twice with Zenit St Petersburg.
Massimo Brambilla served as interim manager for Juventus during the 3-1 victory over Udinese on Wednesday placing them seventh in the Serie A standings - trailing leaders Napoli by six points after nine matches.
Their Champions League campaign sees them in 25th place in the group stage, having lost once and drawn twice in their opening three matches.
