McCall, another Gers hero, was appointed head coach last week, but his first two games failed to break the run of draws that was in progress.
A 1-1 with Livingston on his debut was followed by a 2-2 with Alloa, and he will be keen to get his first victory this weekend - against Hibernian.
Hibs sit six points ahead of Rangers in second place, but a win for the Light Blues would lift them to within three points, and with a game in hand.
That will increase their chances of progressing in the play-offs, and will potentially ease the passage to the Premiership.
Although the opening two results were disappointing, with many expecting McCall to have an instant positive impact, it is no surprise that he could only register two draws.
He has already overseen two games despite being in charge for just eight days, and it is likely that his impact will only start to be felt starting this weekend.
There are clear deficiencies in the Rangers squad at Championship level, and Johnstone, although impressed by some changes McCall has made, still believes there are three areas that the former midfielder must work upon.
“Up front, we are not sharp enough and we don't have enough pace,” the 14-capped Scotland international told the Evening Times.
“Chances are being created but they are not being taken. That is the two basics - defending and attacking.
"At this moment in time, it is very poor. The midfield is struggling as well, they are getting outplayed in there.
“Stuart will want the side to defend better, to close down quicker, as teams are doing to us, and to be more clinical in the final third."