Should Rangers triumph at the weekend it would seal the title at the home of their rivals and reigning champions. But McGrain refuses to entertain such a prospect and instead views the contest as a chance to reduce Rangers' advantage at the top to four points. Should that happen, the former defender believes Rangers might buckle amid the pressure of the three remaining games.
Celtic started the season in turmoil, but in recent months have emerged the form team of the division as their strong run has coincided with jitters across the city at Ibrox. That was until Celtic's 1-0 loss at St Johnstone at the weekend which enabled Rangers to resume control with a 3-1 home success against Aberdeen.
McGrain said: "We all want to win the championship again, but more than that, the supporters, the players, nobody wants to lose it to Rangers at Celtic Park. If we can win then Rangers might hopefully bottle it because if we manage a victory on Sunday it will be a test for them after that in their three remaining fixtures.
"Rangers would have to get themselves together again quickly and should be aware we still have the championship at Celtic Park and want to keep it.We know Rangers want to take the trophy from us, but we will hold on to it as hard as we can - to my mind everything is still possible for us."
He added: "It is one of those games when the result is far more significant than the performance, playing well and losing would be no consolation."
McGrain himself played out a genuine Old Firm title decider on 21 May, 1979 when a 4-2 victory clinched the league for Celtic. He recalled: "A television technicians' strike means few pictures of that game survive, but I still recall it in my mind and remember thinking we'd lost it when Johnny Doyle was red-carded. But we recovered and I remember Murdo MacLeod's clinching strike to this day, we played superbly that night."
Andrei Kanchelskis, meanwhile, has dismissed the pride and passion of Sunday's game as second rate compared to the big grudge match in Italy's Serie A - Fiorentina v Juventus. The Russian international has rejected the widely held belief that a Rangers-Celtic confrontation is the fiercest of all club battles. Instead, Kanchelskis, who grabbed the vital second goal in Rangers' 3-1 victory over Aberdeen at Ibrox on Sunday, insists nothing can compare to the hatred when Juve play at Florence.
The two Italian clubs have a history of bad blood and the dislike became even more intense at the start of the 1990s, when Juve captured Fiorentina's Roberto Baggio.
The player went from hero to hated as the Fiorentina fans rebelled - and, according to Kanchelskis, who signed for Rangers from Fiorentina last summer, relations have not improved. "Fiorentina and Juventus is similar to the Old Firm but the rivalry is much nastier and there is always trouble," said Kanchelskis."The last time I played in that game it was the worst I have ever seen. The game was in Florence and the Fiorentina fans trashed the Juventus bus.
"When the Juventus bus goes to the stadium they come through a tunnel and the fans wait at the other side to throw stones and bricks at it. I watched the bus arrive and all the windows were smashed in and the players looked so frightened. The Fiorentina fans can sometimes be very aggressive and when they lose they really don't like it."