Watford manager Xisco Munoz says the club will begin a "new era" without "legend of the club" Troy Deeney.
The former captain left Vicarage Road during August's transfer window, having been at the Hornets for 11 years, to rejoin boyhood club Birmingham.
Xisco said the 33-year-old will "always stay in our hearts" having scored 140 goals in 419 appearances for the club.
He was pivotal in Watford's 2016 promotion to the Premier League as well as their 2019 FA Cup final appearance.
Deeney, who missed three months of last season with an Achilles injury, was struggling with playing time at Watford and became a free agent last month.