Johnson told the press ahead of this Saturday's big game against Chesterfield that his team have probably a 'five percent chance' of making the top six.
"This is going to be a big one because it's Chesterfield and they're hugging on to that sixth spot," he said.
"I think they're a good side. People that know players, know that they recruited well. I always expected them to be up there. They've got a decent budget really. They've got it going down there and they've stuck at it. They've got good players and the cream always rises.
"It was a disappointing Easter weekend for us. In the big picture, it was probably two games too far. We had a punch on the nose against sheffield United and we went to Colchester hoping to bounce back. I thought we did. I'll stand by the players because I thought for 60-70 minutes we were okay and verging on half-decent. But we drained physically and mentally.
"You have to fight to the death, of course we'll do that. We've done it already and got six wins on the spin. It happens in football. This will be a big one, of course.
"It's a case of this is our first cup final, if you like. We have to make sure we play better than we did against Sheffield United.
"We didn't get a foothold up front against Sheffield United."
The Head Coach only has Lewin Nyatanga as the most recent concern having received an elbow to the eye on Monday against Colchester.
"We're hopeful but not definite," added Johnson of the centre-half. "It was a nasty cut he got to his eye. It really did close up. It was like he'd gone 10 rounds with Tyson!
"We thought about draining it so we sent him to a specialist but it was too close to the eye.
"It's a case of letting the healing process happen. He didn't train today but we'll see how he is tomorrow.
"We have a couple of little niggles. We didn't get any big whacks or swollen ankles or anything like that."
