Jakob Johansson's solitary goal in Solna on Friday gave Sweden the upper-hand in their play-off, setting alarm bells off in Italian football.
That result left the Azzurri on the brink of failing to qualify for the World Cup for the first time since 1958, coincidentally when it was held in Sweden.
Ventura has come under significant pressure as a result and is likely to lose his job should Italy fail to overturn the 1-0 deficit, but Buffon believes their support could give them the advantage and called for them to forget their club allegiances when they head to San Siro on Monday.
The goalkeeper told a news conference: "It's a crucial game for us, for the whole country and for the whole history of our national team as well.
"In my career, I already faced moments like this one, sometimes it went good, sometimes it went bad.
"But it won't change anything about my relationship with the Italian national team. There's no room left for words and wishes.
"It's time to get something on the pitch. I hope the supporters will help us, not having a too negative approach towards us from the beginning.
Ventura was not surprised by the situation Italy find themselves in with respect to finishing with a play-off spot, admitting that he accepted as soon as the draw for the group stage was made that Spain were going to finish top.
He said: "When I took the job I was exactly expecting this scenario; we were aware that Spain could have been stronger than us, we then targeted to be among the four best second teams, and that's exactly what we achieved."