The Italy playmaker was a doubt for Juve's Serie A opener at Chievo on Saturday after sustaining a knock playing in the Trofeo TIM last weekend.
Pirlo was sent for a scan on Thursday and the Serie A champions revealed that he is set for a spell on the sidelines.
A statement on Juve's official website said: "The examination showed a distraction function hamstring muscle tendon that will require 30 days to complete functional recovery.
"The midfielder will continue his rehabilitation program and will be subjected to further investigations in 15 days."
Pirlo's absence is a blow to coach Massimiliano Allegri, who is preparing to take charge of the Turin giants for the first time in Serie A this weekend.
Allegri is also without Alvaro Morata, Arturo Vidal, Andrea Barzagli and Giorgio Chiellini.
