Buffon limped out of a training session on Friday after suffering the knock and after receiving treatment immediately had to undergo sessions of physiotherapy late into the night.
On his personal Twitter page, Buffon urged fans to make light of his absence and support his replacement Salvatore Sirigu in Saturday's Group D battle.
"Life is great... and a missed match or another missed World Cup is not going to change my opinion on that !!" Buffon said.
"And, even if you're not out on the pitch, there are other ways in which you can play an important role. So, go on Salvatore Sirigu !! Go on the lads !! Go on Italy !!"
The loss of Buffon, one of the world's best goalkeepers and a pillar of an Italian side looking to make amends for their first-round exit in 2010 could be a huge blow for Italy.
The Juventus 'keeper played only one half-time in South Africa, coming off with a back injury and being replaced by Federico Marchetti.
Italy drew 1-1 with Paraguay, and with Marchetti between the sticks Italy stumbled badly in their next game, drawing 1-1 with lowly New Zealand.
Italy eventually crashed out thanks to a 3-2 defeat to Slovakia.