The 29-year-old was sentenced to six years in prison last March after being found guilty of sexual activity with a child.
In the footage - published today by The Sun - Johnson is asked if he had sex with the girl and he replies: "I didn't even get my cock out."
A fellow prisoner then remarks that Johnson "didn't even fucking rape her" and the footballer responds: "No, I wish I fucking did for six year."
He continues: "I was going to the home games like, you park your car in the car park and she was at my car every game right, waiting for me, just standing there like in all the gear and that... like tight jeans, little shirt, tits out, not like skirts and that.
"Then after the game she was asking for pictures all the time. This went on for about six months and the next thing she says, 'Can you get us a signed shirt?' and uh... then she added me [on social media].
"I accepted her, got talking to her, I didn't, I didn't know, I just thought she was 17, 18. Got talking to her for a few weeks and then I met up with her and fucking kissed her and...
"And there's lads on here who's fucking shagged like 12-year-olds and got 13 months and that. You know what I mean? They got like half the time!"
Johnson then goes on to say that his best chances of resuming his playing career when he is released will be abroad because of "do-gooders" in England.