Stewart Regan, the chief executive of the Scottish Football Association, has criticised Charles Green for his use of the word 'P***' during an interview last weekend.

The Rangers chief executive has been served with a notice of complaint by the SFA, who have also written to Rangers seeking clarification about Craig Whyte's assertion that he was originally involved in the consortium Green fronted when seeking a route out of administration last summer for Rangers Football Club plc.

Green has until April 17 to respond to the charge, which was raised after he revealed he refers to Imran Ahmad, Rangers commercial director, as "my P*** friend". The hearing has been set for April 25, with Green cited for "bringing the game into disrepute by making comments in a media interview of an offensive and racist nature".

Green, who is likely to face a fine, last night expressed contrition for his comments. "I apologise unreservedly if any offence has been taken by my remark," he said. "I was trying to make the point, albeit clumsily, that I am not a racist. Imran Ahmad is a close friend and business associate and I would certainly have no cause or wish to offend him."

The remark was referring to moments when Green would share a joke with his friend, but his use of the word, "P***", references to a former team-mate who he called "Darkie Johnson" and attempts to justify the language were hugely damaging. In combination with Whyte's allegation that he believes he was part of the consortium Sevco 5088, Green faces a period of crisis.

Show Racism The Red Card condemned the comments, while the SFA's charge refers to the Disciplinary Rule 66 and Rule 71, which guard against comments which bring the game into disrepute and those which are not in the "best interests" of the SFA.

"It's very surprising and it's frustrating when we are all trying to build a stronger and more positive game," said Regan. "It's not helpful for anybody to be using the kind of remarks that were used but we need to give Mr Green the chance to explain himself and that's what we have done. We have written to him to ask him for his feedback and for the background to comments he made and until we have that it would be wrong to speculate on what happens next."

As part of their undertaking when applying for the transfer of Rangers' SFA licence last summer, Green pledged that Whyte was not involved and would not be in the future. The business and assets were sold to Sevco Scotland, but Whyte claimed that £137,500 paid into Ahmad's mother's account was funding towards Sevco 5088, another company created by the consortium Green fronted. The money remains in the account, and Whyte has refused to facilitate its return.

An associate of Whyte's also sent a £25,000 cheque to Green to go towards legal fees, although that subsequently bounced. Whyte alleges the payments are proof of his involvement in Sevco 5088, and that Green was a front for him. He says that he intends to launch a legal case claiming rights to the assets sold from RFC plc in liquidation to Green's consortium.

The SFA – who have banned Whyte from involvement in Scottish football – have sought an explanation of Whyte's claims, with Green having asserted that they were merely stringing him along to secure his majority shareholding.

"We have to seek the facts and that's what we've done," said Regan. "We've written to Mr Green, as chief executive of the club, and asked him to respond to a number of very specific points about the revelations last weekend. And once we've got those answers, we'll be able to decide how we deal with it."

Last Friday, Ticketus won their legal case for £17.7m against Whyte. There was further bad news for the former Rangers owner when police launched several raids yesterday in connection with their investigation into Whyte's purchase of the club from Sir David Murray in May 2011. Rangers have also begun legal action against Whyte's recent allegations.

"A letter has been received and, as we have already stated, matters relating to Craig Whyte's allegations and claims are being dealt with by our lawyers both here in Scotland and in England," the club said in a statement relating to the SFA seeking clarity. "We are entirely comfortable with our position and a full response will be issued to the SFA in due course."