The Juventus playmaker suffered a clash of knees in Sunday's Serie A victory over Udinese and initial reports have suggested that he could miss a month of action
The Bianconeri have not indicated for how long the 34-year-old could be sidelined but reports suggest that it could be up to a month, potentially ruling him out of the rest of 2013.
"Andrea Pirlo, who picked up a knock not long after kick-off in yesterdays fixture between Juventus and Udinese, has undergone medical tests this afternoon," read a club statement released on Monday.
"The examinations at Turin's Fornaca Clinic have revealed second-grade damage to the medial collateral ligament of his right knee."
The playmaker was involved in a clash of knees with Udinese midfielder Andrea Lazzari during the 1-0 victory over the Zebrette on Sunday.
Pirlo suffered the knock after only six minutes and attempted to run off the injury before signalling to the bench that he was unable to continue after 15 minutes.
Juventus's win over Udinese, courtesy of Fernando Llorente's last-minute winner, stretched their lead in Italy's top flight to three points.
The Bianconeri face Bologna on Friday before a crucial Champions League clash against Galatasaray.