The assistant manager to O'Neill made the return to his former club last season but already the former Republic of Ireland coach is looking for a new challenge.
"Working with Martin over the last few years has been a magnificent experience, one of my greatest in football both as a player and a coach and one I want to personally thank him for," he told the club's official website.
A statement from Forest added: "Roy would like to express his gratitude to the club's owner, board of directors, the staff, the players and in particular manager Martin O’Neill for the opportunity to return to The City Ground."
Forest finished ninth in the Championship table last season and are expected to be challenging in or around the playoff places next term.
The east Midlands outfit are 5/1 to be promoted, while the Reds are 16/1 to win the Championship title outright.
Arch rivals Derby County are 16/1 to win the title next season.
View all Soccer betting
The assistant manager to O'Neill made the return to his former club last season but already the former Republic of Ireland coach is looking for a new challenge.
"Working with Martin over the last few years has been a magnificent experience, one of my greatest in football both as a player and a coach and one I want to personally thank him for," he told the club's official website.
A statement from Forest added: "Roy would like to express his gratitude to the club's owner, board of directors, the staff, the players and in particular manager Martin O’Neill for the opportunity to return to The City Ground."
Forest finished ninth in the Championship table last season and are expected to be challenging in or around the playoff places next term.
The east Midlands outfit are 5/1 to be promoted, while the Reds are 16/1 to win the Championship title outright.
Arch rivals Derby County are 16/1 to win the title next season.
View all Soccer betting
Source: bet365.com