The 27-year-old Guerrero tore the medial ligaments in his left knee during Hamburg's 1-1 draw with Borussia Moenchengladbach on Saturday and will miss the south America championships to be held in Argentina from July 1-24.
He picked up the injury in a tussle with 'Gladbach midfielder Marco Reus, who has been called into the Germany squad for the home friendly with Uruguay on 29 May. His club Hamburg report the forward, who has won 29 caps for Peru, does not need an operation, but will be out for between four and six weeks.
Meanwhile, compatriot Farfan is back in the Peru squad following a ten-month absence after he was suspended in October 2010 following a 1-0 defeat to Panama after leaving the team hotel for an unauthorisation trip to a casino.
Peru trainer Sergio Markarian has included the 26-year-old Die Konigsblauen winger in his squad for a warm-up tournament in Japan from 1-7 June when the Peruvians will face their Japanese hosts and the Czech Republic.
Peru face Chile, Mexico and Uruguay in Group C of the Copa America.