The 21-year-old Argentinian only joined City this summer in a £3million move from Racing Club.
Zuculini did feature regularly in pre-season and was a substitute in the Community Shield loss to Arsenal at Wembley earlier this month, but the club feel he could develop better fighting for a place at Valencia.
A statement from the Spanish club read: "Valencia and Manchester City have reached an agreement for the transfer of footballer Bruno Zuculini until June 30, 2015.
"Bruno Zuculini is one of Argentina's most promising players. He made his debut in the Argentinian first division aged only 16 and he comes with the purpose to contribute to the team's midfield in this exciting new Valencia team."
- Sports & Recreation