Barry Ferguson is adamant no matter what issues Celtic faces in getting a new manager, Rangers must go full steam ahead in halting their arch-rivals' dominance.
The former Ibrox skipper has called for his old to 'restore natural order' in Glasgow.
The ex-Kelty Hearts boss is pleased with the business Michael Beale has carried out so far in the transfer market.
And while some Gers fans may be celebrating Postecoglou leaving Celtic, he insists that there's no party to be had as it doesn't change Rangers' task in hand.
He wrote in his Daily Record column: "This is no time for anyone at Rangers to take their eye off the ball.
"Yes, I absolutely get it. The sight of Ange Postecoglou leaving Celtic for Spurs will have delighted some of my old club’s supporters. But I’m not one of them.
"When I wrote last week that I didn’t want the big Aussie to quit for Spurs I meant every word of it because I wanted Michael Beale to stand up to the challenge from across the city and then overcome it.
"Put it this way, Celtic’s decades of dominance are not going to be ended by default. And it’s worth remembering that, while Postecoglou claimed five out of six trophies in his two years at Parkhead, this was just the latest part of a pattern that stretches back way longer than a couple of seasons.
"In total, that’s 17 trophies they’ve picked up over the last seven campaigns. Just let that sink in for a moment. From the 21 that have been up for grabs over that period, they’ve stuck 17 of them in their own trophy cabinet.
"And if anyone at Ibrox thinks that’s even close to being considered acceptable then they don’t deserve to be inside the building.
"So let’s be very, very clear. This dominance has to stop. And there’s no point in Rangers celebrating Postecoglou jumping ship into the English Premier League when their own house still needs putting in order.
"No, Rangers are going to have to earn the right to get back to the top of the Scottish game by their own actions. They won’t just land there by getting lucky. And even if they do, they certainly won’t stay there for very long.
"Picking up the odd trophy every now and then is simply not the way my old club was built. I was brought up to accept that delivering anything less than one or two pieces of silverware a season would be looked upon as a failure.
"That may sound a bit demanding to some of the current players but the sooner the attitude returns, the better.
"So don’t waste any time laughing up your sleeve because Big Ange has left the premises. Get your finger out and get on with the job of restoring the natural order.
"And don’t even think about letting complacency creep into the equation because the chances are that Celtic will replace Postecoglou with a manager who is every bit as capable.
"The very mention of Brendan Rodgers being in the running for the job should send a shiver down the spine because he’s the guy who started this monopoly by leading them to three successive trebles.
"Now I don’t know if Rodgers is ready to return or not but, whoever is brought in, it won’t change what is required at Rangers.
"So, while Celtic now have their own issues to deal with, Beale has been busy getting on with his business, preparing for what was going to be needed to knock Postecoglou off his perch. The face in the opposite dugout might have changed and I am genuinely sorry about that because the Australian was a breath of fresh air.
But the challenge facing Rangers remains exactly the same. They can’t allow themselves to be distracted from the ultimate end game of returning the club to the place where it belongs."
