Blackman has left Bristol City by mutual consent.
The 18-year-old utility man signed a two-year deal at Ashton Gate in the summer following his release from Portsmouth.
He made just two appearances for the Robins, both in the Carling Cup, but has not featured at all in their Championship campaign.
Robins boss Gary Johnson confirmed both parties decided to part ways.
"It has been a mutual agreement and we wish him well for the future," Johnson told the club's official website.