Eriksson tried to help Johnson get back on track when he was manager at Leicester, taking the lad on loan for seven uneventful games. When Eriksson left the Foxes, so did Johnson, and he has not played since, with City terminating his contract in December.
Speaking to Swedish newspaper Expressen, Eriksson said: "I had him as a young gun at City and everyone was talking about him as the next big star in the English national team.
"But then he got injured for a long time and after that, something happened. I've heard about his problem outside the pitch, with alcohol. I hope he will find himself again. When he came back from injury, he was with the reserves - after that I brought him to Leicester but it wasn't working out.
"When I left Leicester, they told him to leave the club.
"He is a really nice boy, I like him, and it's sad he isn't playing.
"Didi Hamann said he was the best midfielder he ever played with. Well, you can understand that - he was a very talented boy."