The US forward was witnessed rowing with coaching staff in the tunnel and emotions boiled over in the dressing room where the forthright exchange of views led to Cathro and Johnsen having to be split up.
Johnsen, who has scored just one goal in his last 20 appearances, was immediately replaced by Rory Currie and failed to re-emerge for the second half.
That paltry goal return, combined with this breach of discipline, leaves the 25-year-old’s future at the club in jeopardy, despite the fact he still has two years left on his contract. The players were understood to have been given the day off yesterday but Cathro will face the media today.
A major signing target for former head coach Robbie Neilson last summer, the 6ft 4in Johnsen has shown promise, winning the Ladbrokes Premiership Player of the Month award in November, but he has struggled under Cathro.
Only a few days ago he spoke of his difficulty in adapting to the tweaks in style imposed by the Hearts boss.
“I have not been able to get on the pitch because I have not trained well,” Johnsen said. “That comes with the relationship with the manager too. I need to know what he wants from me and that I am someone who could be used positively in his formations. It is a different style from Robbie Neilson who was very direct and I knew when the ball was coming and where to be in that moment. Now it is a little bit different because there are different timings and waiting on play to develop.”
The lack of goals has become an issue in recent weeks, with Cathro frustrated to lose or draw games he feels the team were worthy of winning. It has led to a results tally of just six wins in 25 games and has contributed to the club missing out on a Europa League qualifying place.
On Wednesday night they suffered another defeat, at the hands of St Johnstone, leaving them without a post-split victory in four matches.
On Sunday they face champions Celtic before the curtain comes down on a disappointing season and eyes will be on the Hearts line-up to see if Johnsen has been omitted from the squad.