Sir John Hall says Mike Ashley has "fallen out of love with Newcastle" and believes bad advice has led to his underfire treatment.
The 85-year-old sold the rest of his 41.6% shares to Ashley back in 2007, which proved the stepping stone for the Sports Direct owner to acquire full ownership of the Tyneside club.
In Ashley's 11 years at St James's Park, he has overseen two relegations to the Championship, plus several protests, the latest being his decision not to back boss Rafa Benitez in the summer transfer market.
On October 16 last year, Ashley decided to put the club up for sale and announced he hoped to have a takeover completed by Christmas, however on year on, he remains at the club.
Despite a takeover seemingly no closer to happening - Hall believes Ashley is "serious" about selling because he no longer loves Newcastle - and the only reason he hasn't handed over ownership is because no one has met his £300million asking price.
"I think he is serious in his intention to sell, but there aren't many people with the sort of money to buy it off him. There certainly isn't in the North East, anyway," said Hall, speaking during an appearance with the Magpie Group at a Newcastle Legends event in aid of the West End Foodbank.
"There has definitely been interest in the club, I know that, but clearly nobody has yet given him the price he wants.
"If you have fallen out of love with your business, you have to sell - and I think Mike's fallen out of love with Newcastle.
"If someone wants to buy a football club, they will come along and do it. It won't be a long, drawn-out process done in public.
"But, until someone offers what Mike wants - whatever figure that is - then the club won't be sold."
Ashley ended Hall's 15-year spell at Newcastle - where the once property developer insisted he thought Ashley had plans to develop the club and grow his business across the world.
Instead, the Magpies have appeared on the European stage just once under Ashley in the 2012-13 campaign and have often competed with the ambition of just avoiding relegation.
Hall added: "He had the intentions of taking the club forward. That's what he told me, anyway," Si
"He told me he wanted to use the club to help grow his business in East Asia, which I thought would benefit everyone because it would mean Newcastle United would gain a wider fanbase, and grow too.
"But things went wrong - he received some bad advice which led him to make poor decisions - and he's never been able to wrestle that back. I'm sad it hasn't happened how he thought it might."
Meanwhile, Hall believes a potential owner will need to spend £300-400million in order to make the Magpies competitive again.
"People coming into football now do so not because they love football, but because they smell money," Sir John added.
"But, when it comes to Newcastle, you will need to spend £300m or £400m to buy the club, and then another £500m over five years to really make the club competitive if you want to change Newcastle's fortunes.
"It's not just about who comes along; there has to be success or they have to be able to bring success."