Midfielder Ben Watson admits he jumped at the chance to join Watford's promotion push, after joining from Wigan.
West Brom have completed the signing of Callum McManaman from Wigan for an undisclosed fee.
The 33-year-old striker signed a new one-year deal last summer under then-boss Paul Jewell but has only featured once off the bench since the appointment of Mick McCarthy in early November.
Scotland will now look to gain regular first-team football elsewhere.
McCarthy told Town's official website: "Jason is a fantastic guy and has been great around the training ground but we are going younger and he's been missing out.
"He understands that and wants to go out and play football at the twilight of his career. We wish him well."
Scotland joined Ipswich from Wigan in 2010 and enjoyed close to 100 appearances in total, scoring 21 goals.