Johnson failed to make an impact at Chelsea during an unhappy spell at the club under Jose Mourinho.
The England international joined Liverpool in a £17million deal from Portsmouth this summer.
“Chelsea was a big stage for me and it was all working out perfectly until Jose Mourinho turned up,’ admitted Johnson.
“He had his own plans and wanted to bring in his own players, and that was the start of my downfall as a Chelsea player.
“Some players might have been happy hanging around and picking up their wages, but that’s not my style.
“I knew I wasn’t going to be impressing anyone sitting on the bench or even being left out of the squad altogether.
“I never had a word of explanation from Mourinho, but I soon decided I couldn’t take any more. I never had a chance under him. It was one game every four or five and you can’t develop any form or consistency that way.
“I had to leave, even if it meant taking a step down at Portsmouth. As it turned out, they were great for me and I loved every minute there.
“But perhaps I deserve some credit, too. Some players might have folded, but I always knew I had fire in my belly and the self-belief to get back to this level.
“I don’t bear any grudges against Mourinho. That’s life – you get on with some people but not others. But I will be looking forward to the Champions League draw with interest.”