Johnson could be back in action within a month, but the severity of his knee injury meant he was left out of the club's 25-man Premier League squad at the end of January.
It appeared likely, at the time the squad was confirmed, that Johnson would be out for the rest of the season but he confirmed on Thursday that he is on the verge of a return to full training.
The 32-year-old, plagued by injury in recent seasons, suffered cruciate ligament damage against Chelsea in September in only his third game for the club.
"The knee is great, I've been working hard in the gym and finally got outside a couple of weeks ago," he told the club's official website.
"I'm not too far away now. I went to see the surgeon and got the go ahead now to crack on to the next stage. Hopefully within the month I will be back training with the boys.
"Because of the 25-man system this year I haven't been named in it so it is impossible for me to play this season.
"It would just be great to get a couple of games under my belt with the reserves and have six weeks or two months training with the first team.
"There is no denying that the team have been going through a tough patch. Of course it is frustrating being in the treatment room knowing you can't have an impact on the outcome of what is happening."