Hearts: Ian Cathro appointment was mistake - Gary Mackay
The 31-year-old, who took over in December 2016, is under increasing pressure after the Jambos were knocked out of the League Cup on Saturday.
"Look at it from December, it's been a mistake, no-one can question that."
That result came in the wake of a 2-1 defeat by League Two Peterhead in the competition last week.
And, with Cathro - in his first head coach role - having overseen a poor run of results last term, Mackay says the club's director of football Craig Levein should act now.
"Craig is a stubborn individual. It took him a long time to admit he made a mistake playing 4-6-0 as Scotland manager in the Czech Republic."
Owner Ann Budge and Levein both had to leave their seats in the stands before the Saturday's penalty shootout because of anger from fans around them.
Mackay said: "Ann Budge has come out from the very beginning and said that Craig is in charge of the football department. If you're in charge of the football department then you have to be answerable to what happened on Saturday.
"I didn't like the scenes. I didn't like that it looked like Ann and Craig had to be shepherded away before the penalties, but that is just an impact of the results since (former head coach) Robbie Neilson left the club.
"It's not nice, Ann comes out and faces things, she interacts with the supporters. Craig does a thing at the end of every season with the press, but there has to be more interaction so that supporters have an idea of what's going on behind the scenes, because now we have no idea."
Mackay, who made a club record 737 appearances for Hearts, fears Cathro has lost the dressing room.
"Ian Cathro's point is massive that as a head coach he talks about improving players and the team, and you can do that," said the 53-year-old.
"What he said after yesterday's game was that Dunfermline wanted it more and that comes from the changing room. Allan Johnston and Sandy Clark were able to get more from the Dunfermline players than Ian Cathro and (assistant) Austin MacPhee were able to get from the Hearts players.
"Finishing third in their group with three part-time teams is not good enough for a club of Hearts' stature.''