Celtic chief executive Peter Lawwell believes fans would continue backing the club in big numbers in the absence of Old Firm rivals Rangers.

The future of the Ibrox club is in doubt after legal papers were filed with the Court of Session in Edinburgh yesterday signalling Rangers' intention to enter administration, as they await the verdict of a tax tribunal.

The HMRC case centres around the use of employee benefits trusts (EBTs) which were in place before Craig Whyte took over as chairman from Sir David Murray last May, with Rangers looking at possible "liabilities and penalties substantially more than the £50million reported".

The possible demise of the club altogether has also been raised in the media, leading to questions over Rangers' historical relationship with Celtic and the very future of the game in Scotland.

Asked if Celtic fans would continue to support the club in the same numbers in the absence of the Old Firm rivalry, Lawwell told Press Association Sport: "Absolutely. It is a changing world.

"Nothing stays the same and our job is to make sure we are still seen as a big important club in Europe and if there is any change we are part of that."

As for the potential for a European League, Lawwell said: "Who could say? Possibly, or a extension to the Champions League or an extension to the Europa League.

"That's where we are with it all. We are looking long term.

"I think we are doing all the right things. In saying that, we are still to win [the league], we are not getting carried away or gloating or getting ahead of ourselves.

"We know what we have to do, we have to deliver and then hopefully this long-term strategy keeps the fans coming, keeps them interested and connected with Celtic.

"And I think they have, Neil (Lennon) has done that and season books are up this year."

Lawwell was speaking yesterday following the release of Celtic's interim financial results which he described as "very satisfactory".

Celtic reduced their bank debt by £2million during the second half of last year, with turnover increased by 3.1% to £29.3million.

The club made a pre-tax profit of about £180,000 while cutting the debt to just over £7million, a figure chairman Ian Bankier described as "very manageable number" among a "robust" set of figures.