Sir David Murray, the Rangers chairman, last night challenged would-be investors to come forward as he responded to the welter of criticism generated by the sale of Carlos Cuellar to Aston Villa.

Sir David Murray, the Rangers chairman, last night challenged would-be investors to come forward as he responded to the welter of criticism generated by the sale of Carlos Cuellar to Aston Villa and the club's European exit.

In an in-house interview aired yesterday, Murray reiterated his desire to leave after a 20-year tenure as chairman and majority shareholder of the club. He also defended the manner of Cuellar's 10m transfer to Villa Park and was pointedly nonplussed by any implication of responsibility in the defeat to FBK Kaunas that cost the club £10m in potential Champions League revenue.

Murray has been the focus of supporters' disgruntlement after Cuellar invoked a little-known escape clause to join Martin O'Neill's side.

It has prompted renewed calls for Murray to stand down and threats of a protest being staged outside Ibrox before Saturday's Clydesdale Bank Premier League match against Hearts.

Murray has been eager to engineer a departure for two years. David Burnside, a prominent Unionist member of the Northern Ireland Assembly, headed a consortium of London-based businessmen who had investigated a possible takeover. Sir Tom Hunter, Scotland's richest man, has also been historically linked with investing in the club, but his global business and philanthropic interests will preclude any involvement in football.

It would cost in the region of £50m to assume Murray's 90% stake in the Rangers and while he acknowledged the complications of an uncertain economic climate, the chairman admitted two decades at the helm have been more than enough.

"I have heard people say this or that but maybe they should come up to the mark and put their money where their mouth is, then perhaps we can talk," he said yesterday. "I hear people . . . I'm told there are people . . . phoning in and saying Murray must go' and it is obvious that one day I have to. My family would love me to leave but I will not leave this club until there is someone capable of taking over and keeping the club in safe hands.

"When you have been in charge for 20 years, which is far too long for one person to be involved in football, question marks are raised. In our heart of hearts, we know we have collectively done our best."

Murray defended the sale of Cuellar, six months after a reticent Alan Hutton was flogged to Tottenham Hotspur for £9m. He insisted the club were powerless to prevent the 26-year-old activating his release clause but promised Walter Smith maximum support before the summer transfer deadline.

"There is nothing untoward and Carlos will confirm that himself," said Murray. "When we signed him for 3m, we never thought we would sell him for 10m a year later. It is a straight deal, a clean deal, there is no percentage going to other clubs. It is a good deal financially but football-wise it's not.

"The question has been asked if he was forced out but the fact is the chief executive Martin Bain sent out a clear statement explaining the situation. People always want to put their own twist on it. We are disappointed to lose him but we will take the money and hopefully spend it wisely in the short term. It would have been a lot better if we knew this Cuellar's intention to leave a few weeks ago when we could have had more time, instead of trying to rush about, but we accept that's football.

"We will spend the money, we have promised to do that, but what we mustn't do is try to spend it before Saturday and put ourselves under pressure."

Murray bristled at his implication in Rangers' off-field woes. He spoke in exasperated tones of the criticism of the club's new era of financial prudence, after the widespread condemnation of allowing its debt to rise to around £80m.

"It goes with the title," he said. "If I have done something wrong, then I am open to criticism, but I would like to know what I could have done differently. Regretfully, I am judged on football results but as we reach a very difficult financial era in business and in life in Scotland, what is important is that we need to run the club fiscally right.

"We have had criticism in the past for taking too many risks; now we are trying to heed the advice everybody gave us at the time and run it fiscally correct and are still being criticised."

Murray's state of the nation address was laced with references to the internet age of fans' forums, about which he is understood to both obsess and lament. He dismissed speculation perpetuated on such sites of an alleged spat between Ally McCoist and Bain and disregarded the general doom-laden posts that have sprouted since defeat to FBK Kaunas.

"The problem we have is we have a web culture and a media culture today where they don't have relationships with the clubs any more and people want to make the situation worse," he said. "It goes with Rangers. Yesterday, we had people posting things like internal fights and people coming in that just were not true. They know there is no truth to it but they want to cause mayhem. It makes us even more determined to get things right. It's easy to pick on all the negatives but the vast majority of fans understand what we are trying to do and are supportive."

None the less, Murray acknowledged the progress made last season - sustaining a championship challenge until the final day and reaching the UEFA Cup final - has been unravelled by subsequent events. "There is no doubt we are all disappointed with the start to the season and the manager has made it clear that all the good work in the last 18 months was lost against FBK Kaunas home and away," he said. "You can analyse it as long as you want but the fact is the Rangers fans are disappointed."