The Ibrox gaffer has been heavily criticised in the aftermath of his side's embarrassing 2-1 home defeat to part-timers Annan last Saturday.
And despite the high regard the 50-year-old is held in, many Light Blues fans want him out.
However, SportTimes columnist Johnstone believes his friend and former team-mate is deserving of a chance to strengthen for next term.
Rangers can bring in players for no money from September 1 despite the 12-month embargo they had imposed on them by the SFA last year.
And DJ reckons McCoist will leave of his own accord – if matters fail to improve significantly on the park in the 2013/14 campaign after he has recruited new players.
He said: "Only certain people can manage a club like Rangers. Given the state the club are in, Ally needs to be given time to take them on.
"If it is not working next season then people will have a choice to make. He will have been in the job for a few years and will have brought in a few players.
"But Ally will not need to be told. Nobody is bigger than the club.
"If he feels he can't take the club forward he'll allow somebody else to come in."
Johnstone added: "The club is 17 points clear at the top of the table. But still the 45,000 fans who go to games at Ibrox are expecting more.
"In the last couple of weeks more and more Rangers fans have been calling the radio phone-in and saying they are unhappy and want change.
"But better players will be coming in. Ally missed out on his first seven or eight targets last summer. He was unable to convince many players to drop down to the bottom tier. He had to go down his list to get players.
"Rangers may be playing in front of full houses at Ibrox, but players don't want to play in the Third Division. That was the problem in getting new faces in.
"But there will be better players brought in to the club in September.
"There will be new defenders, midfielders and forwards arriving and performances will improve as a result."
Rangers take on Elgin City in the Irn-Bru Third Division at Borough Briggs tomorrow – and they must win if they want to ease growing pressure on their boss.
Johnstone said: "The players have to stand up and be counted. Season ticket renewals are coming up and Rangers aren't sure what league they are going to be playing in.
"If they are in the bottom 18 then is that going to entice punters to buy season books again and go along and watch what they have been seeing?
"The players haven't been performing in recent weeks. Many of them have downed tools. They need to start to produce the goods."