A five-member panel of Brazil's Superior Sports Justice Tribunal Wednesday voted 3-2 against the Peru international forward, whose suspension is a blow to Corinthians' hopes of a top-four finish, reports said.
Guerrero had been acquitted of the charge by the same tribunal last month but faced a fresh trial after prosecutors lodged an appeal.
The incident occurred during a Copa do Brasil match in August, when Guerrero collided with referee Leandro Bizzo Marinho during Corinthians' 1-0 victory over Bragantino.
The 30-year-old former Bayern Munich forward said contact had been accidental and without malice. The decision rules him out of Corinthians' matches against Palmeiras, Coritiba and Santos.