McInnes has been the bookmakers' favourite to take over at Rangers since Caixinha's departure but Aberdeen denied them permission to speak to the 46-year-old on Tuesday.
It is understood that McInnes will meet with Dons chairman Stewart Milne later on Wednesday to discuss his future.
Sources close to Rangers have insisted that they have the cash to pay the compensation fee for both Derek McInnes and Tony Docherty, which would rise to more than £1 million if McInnes joined Rangers and took his No 2 with him.
What is clear is that Milne is determined not to lose his boss to his club's main rivals for second place.
While it seems likely that Rangers will be granted permission to speak with McInnes in the coming days, issues over staffing structures, proposed budgets and expectations mean his appointment is by no means cut and dried.
Widely believed to be a shoo-in for the Sunderland job in the summer after the Black Cats kicked off talks with him, McInnes opted to stay in the Granite City.
Ferguson, 39, played alongside McInnes at Ibrox between 1995 and 2000, captaining the Light Blues to 5 Scottish Premier League, Scottish Cup and Scottish League Cup apiece, including a treble in 2002-03.
But if McInnes does not get his chance at Rangers, will McLean go elsewhere?
The request to speak to McInnes came after a week in which Aberdeen lost twice to Rangers in back-to-back Premiership fixtures with the Ibrox side under the temporary stewardship of Under-20s coach Graeme Murty.
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