Flowers also criticised the clubs current owners Gulf Finance House (GFH) for favouring the offer from Italian Massimo Cellino, who now looks the favourite to takeover the club.
Flowers was locked in talks with GFH in London on Wednesday, but has bowed out of the race to buy the Yorkshire club.
The decision paves the way for controversial Italian Cellino to take control, having already agreed a deal in principle for a 75% stake in the club for a reported £25million, subject to approval by the Football League.
Flowers said in a statement: “I entered discussions in good faith to buy this club for the simple reason that I am a lifelong supporter and sincerely believed that I could make a real contribution towards the goal of promotion to the Premier League and at the same time provide the stability and sound financial governance the club desperately needs.
“However, the emergence of Mr Cellino’s bid, and the nature of the transaction, seems to have crystallised the attitudes of both GFH and the Leeds United board, enabling them to dispose of the club with no consideration for its ultimate security and wellbeing.”
Flowers also claimed the sale is “not in the interests of Leeds United, its players, staff or loyal supporters”.
He added: “Both myself and my company, Enterprise Insurance, have been enormous financial supporters of the club for the last few years and … we remain firmly convinced this deal will not give the club the stability or investor commitment it badly needs.”
GFH declined to comment.