Johnson played with Berahino for the Potters between 2017 and 2018 before the former Liverpool defender retired.
Johnson told talkSPORT: "To be honest it's not so much what's gone wrong, it's quicker to say what's gone right. He had the wrong mentality and the wrong attitude from day one.
"I only know him from the days at Stoke, his days at West Brom, he had a few good months he was hitting the net regularly.
"For whatever reason when he was at Stoke he was always going against the grain. If we were told to be there [at training] at 10, he would turn up at 10 past 10.
"If we were told to wear this, he would deliberately wear something different. It was almost like he had a vendetta against them from the start.
"It was strange to watch really. In training you would see glimpses that he can play. There is something there but he didn't even want to push himself.
"If they wanted us to run faster he would go slower. I am not exaggerating, it would be the same every single day.
"If you were not in the squad, you would have to run after the game. Of course, no player likes doing it because they are angry you weren't playing in the first place.
"You might be running at half 10 at night on an evening or whatever. I understood why players were unhappy about it but that was the rules, but Saido would jog.
"We would supposed to be off on the following Sunday but because Saido didn't run everyone had to come in the next day, even the players that played the game.
"The next day, Saido called in sick. We were only there because of him and he didn't even turn up.
"It was uproar. Where do you go from that? It's total disrespect to the staff, the players.
"And that's what he was like on a daily basis. And considering they paid him with three years left to go tells you everything you know."
Asked if he liked Berahino as a person, Johnson said: "No. I will be brutally honest. I've played with people who might not be up to the level but they are nice and will work hard.
"He wasn't at the level and he didn't try. It's not happened once has it, it's happened throughout the career.
"He's 26, he should be having a big move right now. He's not played for England. There are reasons for it.
"Everyone pretty much says the same thing. If I was the manager or owner of a club I wouldn't take him if they paid me to play him."