Six points from qualifying meetings with Bulgaria and the Czech Republic would see the Azzurri book their place at next summer's finals with two games to spare.
However, Lyuboslav Penev's Bulgaria arrive in Palermo buoyed by their performance in Sofia 12 months ago, where goals from Stanislav Manolev and Georgi Milanov held a rattled Italy team to a draw.
Buffon, who is looking to match Fabio Cannavaro's all-time appearance record by reaching 136 caps with two more starts, feels another stern examination lies ahead with Bulgaria just four points behind and still gunning for automatic qualification.
The 35-year-old Juventus keeper told figc.it: "I'm reasonably worried, as I am before any game that could be decisive in our qualification.
"We deserve (to qualify) for what we've done up to now, but we haven't got it in our hands yet.
"We need to treat this game with a lot of care and attention so we can take another step forward.
"Bulgaria are an organised team who know how to approach this kind of game - they know how to defend and how to hit you on the counter-attack."
Southampton striker Pablo Osvaldo, then with Roma, scored twice to earn Italy a point in Sofia last September but is suspended at the Stadio Renzo Barbera, along with AC Milan duo Riccardo Montolivo and Mario Balotelli.
Winger Emanuele Giaccherini is back in Italy after leaving Juventus for Sunderland in July, and after a six weeks on Wearside he is concerned about playing in the Sicilian heat.
"People always say that September is a hard month for the national team but I think everyone's in good shape," he told reporters.
"Bulgaria are much further along in their domestic league than we are and caused us a lot of trouble over there a year ago.
"Also, it will be very hot on Friday so we will need to have that extra bit of energy needed to win the game."
Bulgaria boast two of the group's top scorers with PSV Eindhoven midfielder Manolev and Aston Villa winger Aleksandar Tonev tied on three goals each.
As much as Lions coach Penev would like to overtake Italy at the top of the group, his realistic target remains securing the play-off place from the chasing pack.
He said: "Maybe mathematically, if we win three matches then we will go to the play-offs.
"But let us first do a job against Italy before we think about Malta, then Armenia and finally the Czech Republic.
"The players all know what is expected of them and they know it won't be easy. There are some very tough games ahead of us, three overseas and only one at home."