Buffon undergoes knee surgery
Media reports said he would be out of action for up to 40 days.
The Italy number one suffered a cartilage problem some months ago but postponed an operation until after the Champions League group stages.
Following their humiliating elimination by Bayern Munich on Tuesday, Buffon decided to put off surgery for a few days in order to help the team recover but the 31-year-old was powerless in Saturday's 3-1 Serie A defeat by Bari.
Austria's Alex Manninger will deputise in his absence.
Winger Mauro Camoranesi could also be ruled out for some time after going off with a thigh injury on Saturday.
Third-placed Juve made a patchy start to the season under rookie coach Ciro Ferrara but last weekend's home win over Serie A leaders Inter Milan reopened the title race.
The two subsequent defeats piled the pressure back on Ferrara, however, and club president Jean Claude Blanc has twice been forced to give the coach his public backing.
Blanc has come in for criticism from fans with Diego, who sent a penalty over the bar in Bari, the latest in a long line of signings to struggle at Juve since their promotion back to Serie A in 2007 following a demotion for match-fixing.