The Gers gaffer's position has been called into question by some fans after a poor start to the campaign.
The Ibrox side toiled at home to Hibernian in the Petrofac Training Cup and slumped to defeat in their Championship opener against Hearts on Sunday.
Pressure is mounting on McCoist and his players as they look to get their second-tier title challenge quickly back on track against Falkirk tomorrow night.
Ibrox icon DJ said: "There were calls for the manager to go aftEr the game on Sunday, as there were after a couple of games last season.
"The fans want the team to win but you can't win all the time.
"You have to remember, Sunday was the first time Rangers had been beaten at home in a long, long time. Ally knows what is expected of him and what he has to do. No one has to remind him about the demands of this job.
"The Greatest Ever Ranger, John Greig, was sacked as manager so anyone can lose their job at Rangers and Ally is well aware of that.
"But he will continue to work hard and will be determined to turn things around, starting with the Falkirk game."
While McCoist has come in for criticism for his team selection and tactical approach, the performances of some of his tried and trusted stars have also been put under the spotlight by the Light Blue legions.
A number of players have failed to show the form that they are capable of and Johnstone has urged the Gers squad to up their game to ease the pressure at Ibrox.
He said: "Ally has got to pick a team that is good enough to win these games and has got a bit of fight in it.
"I think the fans are looking for that bit of dig, a sign of more effort to get everyone on and off the park on the same hymn sheet. I worry that they're being bullied by other teams.
"Ally might pick players that fans think he shouldn't be picking, but he knows what they will give him.
"He can't afford to be loyal to too many people, though, because, at the end of the day, if he doesn't get results the players won't get the sack, it is the manager.
"And he'll get it in the neck from all directions - punters, former players and the media.
"He has got to sit down and have a real think about the way forward.
"Rangers have to get their act together tomorrow night for themselves and for the manager.
"I would expect a far, far different performance from Rangers on Friday, they have got to.
"But we know that there is only one man who will get the stick and has to carry the can and that is the manager.
"If the players like their manager, they have to start getting their finger out and performing and getting results."