Salah, after being dropped for the Champions League win at Inter Milan for his interview after Saturday's draw at Leeds, has been recalled for today's clash with Brighton.
Johnson, speaking with Tribalfootball.com this week, says he's chatted with Reds players and insists Salah hasn't lost any support from inside the dressing room.
He said: "Usually for a player to speak out publicly, there's a lot more that happens before that moment that's not normally the first place to go to or the point of call - normally that's the last resort.
"Now it's like he can't take anymore because normally you'd have a few bust-ups in private before this moment and obviously we'd never know if that's happened. So I can only presume it has (happened) because when I've spoken to the lads they all say how good of a lad Mo is.
"And when I've met him he's been great and you know you don't get to the level that he has if you don't train your socks off so he seems like the perfect pro, the perfect professional. So for him to have an outburst there must be something wrong behind the scenes for sure and it has been brought up."
Saudi regrets?
It has been suggested Salah's frustration is due to being benched by manager Arne Slot as Liverpool have struggled - and only months after rejecting a mega money move to the Saudi Pro League to commit to a new Reds contract.
But Johnson says: "Well, yeah, but hindsight's a wonderful thing. You know, we'd all wish we'd made certain decisions at the time, but you can only make the decision you think is correct at that time.
"You know, if he's turned down bigger money to stay with Liverpool, it probably was the right decision anyway. He probably had no idea that Liverpool would be struggling the way they are and that his form would dip as much as it has.
"So if he knew that, he probably would have left last year or maybe the year before. But like I say, hindsight's a wonderful thing."
- Glen Johnson was speaking to Tribalfootball on behalf of BetWright