The 58-year-old former striking star revealed in December last year that he was battling pancreatic cancer for a second time.
Now, after consulting with doctors, Vialli will "suspend professional commitments" as he fights the disease.
Vialli said on the Italian Football Federation's (FIGC) website:
"At the end of a long and difficult 'negotiation' with my wonderful team of oncologists, I have decided to suspend, hopefully temporarily, my present and future professional commitments.
"The goal is to use all my psycho-physical energies to help my body overcome this phase of the disease, in order to be able to face new adventures as soon as possible and share them with all of you."
FIGC president Gabriele Gravina said:
"Gianluca is an absolute protagonist of the Italian national team and will be in the future.
"Thanks to his extraordinary fortitude, to the Azzurro and to the affection of the whole federal family, I am convinced he will be back soon.
"He can count on each of us, because we are a team, on and off the pitch."
The former Chelsea striker, who went on to manage at Stamford Bridge, was initially given the all-clear from the disease in 2020, but it returned just a year later.
He was appointed to Roberto Mancini's staff in 2019 and played a crucial part in helping Italy win Euro 2020 last year, beating England on penalties at the Wembley final.
― With AAP.
