Johnson spent the latter part of the season on loan at Sheffield United after a bust-up with Gary Megson but accepted the boss's verdict on his campaign.
"I am gutted but I'd be the first to admit I haven't performed this season, and that is the be all and end all. I can't blame anyone else.
"It is hard to take at the moment. I have got two years left as security on my future but it looks like that is away from Nottingham Forest.
"If the decision is based on football, I haven't been good enough. I would be disappointed if it was a financial decision - but if I had been on £1,000 a week, my performances would not have been enough to keep me on."
Johnson may yet be lining up for Forest next season if a suitable offer is not received over the summer.