"Tomorrow will be the official presentation at Coverciano, it will be the formalisation of a long-standing discourse".
His 45th and final competitive fixture at the helm will come on the final day of the Russian Premier League season when Zenit, now fifth and 10 points adrift of champions Lokomotiv Moscow, entertain bottom club SKA-Khabarovsk at Saint Petersburg Stadium.
He began his coaching career with Fiorentina in 2001 and won the Coppa Italia in his first season even though the club was plagued by financial problems.
Since leaving Etihad Stadium in 2013, Mancini also managed Galatasaray and Inter Milan before joining Zenit in June 2017.
His first match in charge will be a friendly against Saudi Arabia in Switzerland on May 28.
He never became a regular with Italy during his 10-year global career, during which he won 36 caps and scored four goals.
Luigi di Biagio had taken up the job on an interim basis, stepping up from the Under-21 set-up, but he has since stepped back down to accommodate the new man.