Jacko has been missing from action for the last two months, suffering from tendonitis in both knees.
It has stalled the Camden-born left-footer's sterling progress that saw him become a reserve team regular at the age of 18.
"I've been out for two months now," lamented Jacko. "It's got better and the injury is certainly improving, but it's still not pain-free.
"I've got to wait until the pain goes then I can start training. I think we're looking at Christmas, that sort of time.
"It's swollen tendons in both my knees, it started in pre-season. I don't really know what the causes are, it's different things. Sometimes when you've had a rest and then come back to intensive training it can flare up.
"Especially as I might still be growing - that can be a problem. The patella tendons in my knee are swollen on both sides."
Johnnie is becoming increasingly frustrated at his routine that involves little other than ticking over and topping up his general fitness. He admits to getting down, but he does go along and support both the first and reserve teams.
"I played the first two reserve games of the season and we're nearly half was through the season now and I haven't played another one!
"It's my first injury and you get down. I go and watch the games on a Saturday and the reserve games, and get frustrated at not being able to play.
"I've just got to stick with it really, continue with the rehab and do some weights.
"I went to see a surgeon and he said the best thing was to rest it and hopefully let nature take its course. There is always a chance of coming back to training, it flaring up, and then having the operation. The main thing is to avoid surgery at my age really - I could do without that."
After playing for both the under-19 and reserve sides last season, he would now relish the chance to get his boots dirty again.
"I played a lot of games last season, I was sometimes playing one day and then the next - with the England games as well I found it quite hard.
"Now I'd take any game I could play in!"
Young midfield starlet Johnnie Jackson is currently living through every player's dread - coping with the frustration of a long-term injury.