Coles, who turned 26 yesterday, had been on loan at Danny Wilson's Hartlepool, for whom he made three appearances.
He now goes straight into another loan deal, going to League One strugglers Bristol Rovers. He's already training with the club, and formalises the deal after a medical today. Manager Paul Trollope has the option to make the move permanent when the transfer window opens in January. The defender is out of contract anyway at the end of the season.
Coles has made 31 league appearances for Hull City, the last of those being on the opening day of the present season. Prior to that, he made 148 league appearances for Bristol City, the club he joined as a trainee and even captained, before his £200,000 move to Hull.