The 32-year-old was withdrawn after 71 minutes of the 1-1 international friendly in Milan on Friday and has subsequently returned to Turin.
Barzagli had an MRI scan on Saturday that confirmed the problem, with the defender now facing a race against time to be fit for Juventus' Serie A visit to Livorno on November 24.
A statement on the club's official website read: "Andrea Barzagli, who left the field towards the end of last night's Italy v Germany game due to muscular discomfort in his left thigh, has undergone an MRI scan this afternoon in Turin which has revealed a pectineus muscle strain.
"The extent of the injury will be assessed over the coming days."
The injury will see Barzagli miss Italy's friendly encounter with Nigeria at Craven Cottage on Monday.
Cesare Prandelli's side have drawn three fixtures in a row, but put in a spirited display against Germany as Ignazio Abate cancelled out Mats Hummels' opener at San Siro to extend the Italians' unbeaten streak against Germany to 18 years.
