29-year-old Collis arrived at Crewe in the summer od 2008 when Steve Holland signed him on a two-year deal and was made Crewe number one keeper.
With the sacking on Steve Holland a few months later Collis found himself out in the cold with new manager Gudjon Thordarson and then with Dario Gradi.
Collis made his final appearance for the Railwaymen in the 5-3 drubbing away to Accrington Stanley and with the arrival of Steve Phillips from Bristol Rovers, Collis became third choice keeper at the club.
Bristol City manager Gary Johnson who know Collis very well from where both were at Yeovil Town told the Bristol Evening Post 'Steve is a player I know very well from my time at Yeovil and he is a very capable keeper.
'Not a lot of people are aware of his situation and he's sneaked under the radar to an extent. We have an opportunity to land ourselves a very good keeper who could provide strong competition for Dean Gerken.
'Our supporters know how good a keeper Chris Weale is and there is nothing between him and Steve Collis. Choosing between the two of them was always one of my toughest jobs during my time at Yeovil.'