The 24-year-old was tipped for a bright future after bursting out of the club's academy system and into the senior set-up, but has seen a succession of injuries severely hamper his progress.
Johnson has become something of a forgotten man as a result, with his last appearance for City coming way back in 2009.
His last competitive outing came for Leicester during a loan spell in 2011/12, but once again he saw injury prevent him from shining at the second tier club.
Johnson broke into the first team at City at the age of 18 in 2006, and was quickly billed as an England international in waiting.
Liverpool were also credited with holding an interest in his services, leading City to offer him a lucrative five-year contract in 2009.
He was, however, to see a series of problems, including a ruptured cruciate ligament, prevent him from fulfilling his promise at the Etihad Stadium
Johnson made just three starts for Leicester in the Championship last season before injury forced his loan deal to be cut short and he found himself in trouble away from the field - as he was twice arrested for drink-driving.
City have now confirmed that the 24-year-old left their books in December, without an official parting of ways being announced.