In June 2007, after great performances with his club Bolívar, he was selected for the Paraguay national football team that participated in the 2007 Copa America. In the quarterfinals of the competition, Paraguay played against Mexico. In the 2nd minute, goalkeeper Aldo Bobadilla was sent off after a bad challenge over Nery Castillo and after Justo Villar got injured earlier in the tournament, giving Zayas the chance to play in the rest of the match and his first cap. Paraguay ended playing the game with 10 players, and they eventually lost 6–0, thus ending the Copa America campaign.
After the Copa America tournament, Zayas was transferred to Guaraní. In 2009 he returned to Bolivia, only this time, he signed with Club Jorge Wilstermann.