28-year-old Collis was signed on a free transfer after his release from Southend United back in June 2008.
The former Yeovil Town favorite signed a two year deal at the Alexandra Stadium and was placed as the clubs number one keeper.
Collis found him pushed down the pecking order after a gaff in the cup game against Millwall in January, his mistake prompted the then new manager Gudjon Thordarson to sign John Ruddy on loan for the rest of the season.
During the summer Thordarson decided to to sign young Spurs keeper David Button on a six-month loan making him the number one keeper with Adam Legzdins as the number two.