Former Rangers manager Walter Smith has said the Glasgow giants should use the bitterness over their forced demotion to the bottom tier of Scottish football as an enduring source of motivation.

Rangers were kicked out of the Scottish Premiership after entering administration in February 2012 over an unpaid tax bill during the short, but chaotic, reign of Craig Whyte.

Liquidation followed in June 2012 to cap an amazing fall from grace for Scotland's most successful club, who have won a record 54 Scottish top flight championships.

A consortium headed by former Sheffield United chief executive Charles Green then bought the club's assets as the Gers were forced to start life again in the country's bottom tier.

Green's tenure was beset by financial upheaval and boardroom infighting and the controversial chief executive was eventually forced out of Ibrox in August 2013.

Last year, both Whyte and Green were among six individuals indicted on fraud charges linked to the takeover of the club in 2011.

But they are now set to return to the top flight after fighting their way back up the divisions and on Sunday they face arch-rivals Celtic in the semi-finals of the Scottish Cup.

Many people connected with the Ibrox club believe Rangers were harshly treated, with Smith among them.

"There was no necessity for Rangers to be put down into the Third Division," Smith said Tuesday.

"That will always stay in Scottish football. There will be a bitterness in the Rangers ranks. It will be a massive motivation for the club. It would certainly be for me.

"How can they forget what happened to them? Nobody could forget that.

"There is no doubt it was the wrong move in my eyes: Scottish football has been worse off.

"And a lot of the teams who were happy to see Rangers going down there have suffered and found themselves relegated or in the process of being relegated."

The 68-year-old added: "Rangers going out the Premier League has, in many ways, caused problems to quite a number of the teams that have been there. And Celtic are one of them, in the sense that they have been left more or less alone to win a championship.

"Aberdeen put up a great fight over the last couple of years but it's very difficult for provincial teams to match Celtic, or Rangers when they were at the level they were at five years ago."

Meanwhile Smith, who helped bring 21 trophies to Ibrox in two spells in charge of Rangers, urged the current board to back manager Mark Warburton in the transfer market.

"Rangers will have to support Mark Warburton in the manner I was supported as manager, to give him the opportunity to challenge.

"The board want the club to be up there and they have to find a way of doing so.

"The economics of Scottish football are fairly straightforward for Rangers and Celtic. If you invest in your team and get to the Champions League, you make money. If you don't, you lose money."