The Italian returns to his homeland - where he spent many a season battling the Bianconeri - two days after being confirmed as the visitors' new coach
Fatih Terim paid the price for a poor start to the season that has yielded just one win in five league matches, as well as the disappointing showing against Real in front of the club's home supporters.
The Super Lig champions were outclassed by the Spanish giants in the Group B opener, with Cristiano Ronaldo once again stealing the show with a second-half hat-trick in the comfortable rout.
Mancini, who has been out of work since being fired by Manchester City in May, took control at the Turk Telekom Arena on Monday.
Galatasaray head into the fixture at the Juventus Stadium on Wednesday on the back of a 1-1 draw at home to Rizespor. Engin Baytor opened the scoring, but Tevfik Kose levelled in the second half before Slcuk Inan saw red.
Midfielder Hamit Altintop continues to be plagued by a hip injury and is likely to miss the visit to Turin.
Reigning Serie A champions Juventus will be desperate to claim a maximum haul after a disappointing 1-1 draw away to Copenhagen in their opening fixture.
Antonio Conte's team are in good form ahead of Wednesday's showdown and are on an eight-game unbeaten run in all competitions.
They will look to build on the momentum from their 1-0 victory over rivals Torino at the Stadio Olimpico on Sunday, with Paul Pogba's second-half header securing the points.
Juve could be without influential striker Carlos Tevez after he picked up an ankle injury against Torino following a robust challenge from Ciro Immobile.
The Argentine has notched three goals in the league for the Turin outfit since his transfer-window move from City.
MasterCard is excited to present episode one of the Priceless Memories UEFA Champions League video series. See what Valencia legend Gaizka Mendieta had to say!