Johnson left Suncorp Stadium injured in the 22nd minute. after picking up a hamstring injury, while trying to chase down Broncos winger Corey Oates.
Just before halftime, the broadcast coverage cut to images of a downcast Johnson, sitting with an ice pack around his left hamstring and his mobile phone in his hand.
Under an NRL policy introduced two years ago, players are banned from using phones in the rooms to eliminate the possibility of inside information leaking and illegal bets being placed.
Johnson acknowledges he broke the rules, but explained he was calling his concerned fiancée - Silver Ferns netballer Kayla Cullen.
"I just called her without thinking and spoke to her," he explained. "It was a tough time and frustrating going through that on my own.
"I let her know I was OK and that's all there was to it. I put my hand up and I did muck up."
Under the circumstances, the 28-year-old, who has never had a hamstring injury in his career, will likely receive a warning from the NRL.
At the time, injured Gold Coast Titans hooker Nathan Peats tweeted that the NRL should have some "common sense", when punishing the New Zealand international.
"When you get hurt, the first thing you want to do is let your partner and parents know you're ok," Peats tweeted. "Not to give information to someone to put a bet on.
"Rules are rules, I understand, but have some common sense."
Johnson could face 2-10 weeks on the sidelines, depending on the severity of the strain.
He joins the Sharks' growing injury ward, which now includes New South Wales quartet Matt Moylan, Josh Dugan, Wade Graham and Aaron Woods.