Andrew Ellis has instructed his lawyers to take legal action against Rangers owner Craig Whyte after claiming he is due a quarter of the club's shares.
Ibrox director Ellis says he was promised a 24.9% stake in the Glasgow club by Whyte when he completed his takeover in May.
"It certainly will not hold up the sale of the club," insisted Ellis. "I'm suing Craig, not the football club.
"I've been trying to sort it out for the last nine or 10 months."
Whyte last week revealed that he had himself taken action through the courts to secure his shareholding.
But the venture capitalist's right to the whole 85% shareholding he bought for £1 from Sir David Murray is being challenged by his former colleague.
"I haven't got anywhere, so I've handed it over to the legal team," said property developer Ellis, who had been involved in a failed takeover bid in 2010 and was appointed a non-executive director by Whyte in January.
Administrator Duff and Phelps is poised to name a preferred bidder this week after narrowing the field down to three interested parties.
The Blue Knights, led by former Rangers director Paul Murray, American tycoon Bill Miller and a Far East group led by Singapore-based businessman Bill Ng are vying for control.
Ng, a 52-year-old businessman with a reported personal wealth of £40m, is chairman of Hougang United Football Club in his homeland.
Miller, a 65-year-old vehicle towing company tycoon, was previously involved in a failed stock car league in his homeland.