The 23-year-old midfielder will be reunited with manager Sven-Goran Eriksson, for whom he enjoyed his best spell at City before three years of injury nightmares.
Johnson, an England Under-21 international, has made 45 first-team appearances for City, but only two since he suffered an abdominal injury in 2008 as he has struggled to get back to full fitness, enduring a series of setbacks.
Source: Team Talk
Source: Team Talk