Despite taking The Hornets into The Premiership, Boothroyd left Vicarage Road by mutual consent after winning just four league games all season and its believed the Watford board have turned their attentions to The Den where Jackett has performed wonders with The Lions, despite many fearing relegation at the beginning of the season.
The Lions boss enjoyed a successful playing career with The Hornets before becoming part of the coaching team under Graham Taylor.
As a result the Millwall manager is now favourite to succeed Boothroyd with Skybet offering 4/1 while Victor Chandler have priced Jackett at 5/1 ahead of Alan Curbishley.