The Italian on Monday signed a three-year contract with the Turkish champions, who parted company with Fatih Terim last week.
Mancini had been out of a job since being dismissed by Manchester City in May but is relishing starting taking Gala to his homeland.
“I am very happy to have arrived to a great club like Galatasaray,” Mancini said. “This is a beautiful and interesting challenge and I believe I have made the right choice.
“Wednesday’s game against Juve will be very important and for me this is a happy coincidence.”
This is not the first time Mancini has come up against Juve in continental competition. While in charge of City, he faced the Turin club in the 2010-11 campaign in the Europa League, with both games finishing in 1-1 draws.
Gala are hoping to make amends for their dismal showing in their 6-0 home defeat to Real Madrid in their Group B opener. That reverse stunned many, including Juventus coach Antonio Conte.
“When I saw the result, I thought something seemed a bit strange so I watched the game and realised it was not a fair score,” he said. “It was too harsh on Galatasaray.
“It won’t be easy because Galatasaray have some top players. (Didier) Drogba is great on the field, a leader and an example.”
Conte has great respect for compatriot Mancini, who led Inter Milan to three Serie A titles. “I rate him as one of the best coaches in Europe and it’s only right that he’s back in the game, and Galatasaray have strengthened further with his arrival. I don’t think Mancini can transform things in a day, but it’s for this reason I’d have preferred to face Galatasaray when I already knew how they would play.”
Juve also endured a disappointing start to the competition with a 1-1 draw at Copenhagen. But the Italian champions head into the contest on the back of last weekend’s 1-0 triumph over city rivals Torino.
Juve are unbeaten and lie second in Serie A, two points adrift of Roma.
Juve striker Carlos Tevez, who played under Mancini at City, has failed to recover from a left ankle wound sustained on Saturday and will not feature.
The visitors are without midfielder Wesley Sneijder, who is out with a muscular injury.
However, Drogba has shaken off a muscular problem to lead Gala’s attack.
In the other match in the group, the world’s most expensive player, Gareth Bale is out of Real Madrid’s match against FC Copenhagen with a thigh problem.
Meanwhile Zlatan Ibrahimovic says Paris St Germain are prepared to send out a message to their prospective rivals that they are genuine contenders for this season’s Champions League. Heading into tonight’s Group C clash with Benfica in Paris, Ibrahimovic insists his side are a different proposition to the one beaten by Barcelona in the quarter-finals last year.
Ibrahimovic said: “After a year in the Champions League the club has more experience. We must show when we’re good and we’ll do everything to beat Benfica and prove we are challengers.”
Bayer Leverkusen v Real Sociedad
Shakhtar Donetsk v Man Utd
Juventus v Galatasaray
Real Madrid v FC Copenhagen
Anderlecht v Olympiakos
PSG v Benfica
CSKA Moscow v Viktoria Plzen
Man City v Bayern Munich.