The firm which acted as administrators of Rangers last year has been cleared of a conflict of interest.
The Insolvency Practitioners Association launched a probe following complaints that Duff and Phelps should not have taken the role when the club went into administration in February 2012.
The complaints were lodged because Duff and Phelps' partner David Grier had occupied an advisory role in Craig Whyte's May 2011 takeover of Rangers.
The probe was launched one year ago and the firm was absolved on Thursday of wrongdoing over the issue.
A statement read: "The Investigation Committee of the Insolvency Practitioners Association has advised complainants of the outcome of the disciplinary investigation into Paul Clark and David Whitehouse, partners of Duff and Phelps and the former joint administrators of Rangers Football Club Plc.
"The complaints centred on whether the insolvency practitioners were in breach of the insolvency profession's code of ethics when accepting their appointment.
"The Investigation Committee, made up of independent practitioners and lay members, has, over the past 13 months, carried out a thorough investigation of the administration of Rangers Football Club and the actions of the joint administrators in agreeing to accept the appointment and has concluded that the practitioners complied with the relevant guidance and legislation."
Duff and Phelps said last year that the probe was launched following a request from the BBC following evidence revealed in a documentary that Grier was aware of a potential deal between Whyte and Ticketus ahead of the takeover.
Duff and Phelps confirmed that fact but stressed that Grier did not know how much money Whyte intended to borrow against future season ticket sales and was unaware that the capital, initially ?24.4million, would be used to pay off the club's bank debt and thus complete his ?1 buy-out.
Rangers were consigned to liquidation in June last year when Her Majesty's Revenue and Customs rejected an offer to creditors.
Duff and Phelps agreed a deal to sell the club's business and assets to a consortium fronted by Charles Green, who quit as Ibrox chief executive last month amid claims from Whyte that he was behind the firm set up to purchase the assets.
Those allegations are the subject of a club-commissioned investigation performed by Deloitte and law firm Pinsent Masons.
Whyte's takeover remains the subject of a police investigation and liquidators
BDO are examining the events which led to the club's financial collapse.
After two days of meetings which were supposed to decide the Spaniard's future it seems what the chairman chooses to do over the weekend will be the significant factor.
Martinez had told Whelan on Wednesday he wanted 24 hours to think about his position but having returned for more talks the 39-year-old's focus seems to have been purely on advancing Wigan as a club.
That has given Whelan renewed hope his manager of four years will not seek pastures new, with Everton, Stoke and even La Liga side Malaga speculated on as potential destinations.
He has now gone away to work out if and how he can bring Martinez's proposals to fruition.
"We have had a good, constructive talk - nothing about wages it is all about the club and can we move it forward in terms of the training facilities and youth development," Whelan said.
"It is all tied up in that. He wants to do certain things and I'm hoping I can assist in that but I'm not going to say I can if I can't and I want to look at it over the weekend.
"If he wanted to move he would've said 'I'm going'. It is nothing to do with his personal benefit - we both want to make the club to be better.
"I have asked him certain questions in terms of what we can develop.
"I don't want to say yes until I've had time thinking about it and things like planning permission.
"It is definitely not that difficult to be spending on the training ground and we have looked very seriously at that.
"We have had some good news from the planning office in relation to what we want to do will be acceptable.
"It will be Monday before I can promise anything."
Wigan are already revamping their academy to meet Elite Player Performance Plan Category One standards but Martinez appears to want to put deep-rooted changes in place to provide a solid base for the club in the future.
Following their relegation from the Premier League the feeling outside the club is the Latics will struggle to get back into the top flight.
But Martinez, whose stay at the club would signal his confidence they can make a swift return, wants Premier League standards applied throughout regardless.
"He is just bothered about the future of the club. It is absolutely for the benefit of the club," added Whelan. "Whatever happens Roberto always wants to improve the club and wants to improve the development with youth - which I agree with entirely."
Whelan insists he is not worried about the future of his manager, with whom he has enjoyed a close relationship since signing him first as a player in 1995 and then again as a manager in 2009.
"We are not losing one bit of sleep over it," he added. "It was quite positive yesterday and I'm hoping, whatever the decision we get, it will be in the interests of Wigan Athletic and that is the most important thing."
