With the arrival of Andy Carroll on a season long loan Maynard was not going to be guaranteed first-team football.
Maynard arrived at the Boleyn Ground in January of this year and only scored three goals for the club in 16 appearances.
The 25-year-old has though, been in fine form in pre-season and scored recently for the Hammers in the 2-0 Capital One Cup victory over Crewe Alexandra.
His departure comes shortly after the Hammers allowed fellow striker Sam Baldock to return to a Championship club.