The Porterbrook Leasing millionaire, who has already had one bid for the club turned down, is thought to be willing to invest pounds 3m-pounds 4m in an offer being put together by former Forest chairman Fred Reacher and two other directors, Keith Gibson and Jamie Mellors.
The move comes just days ahead of a crunch meeting next Monday when Forest shareholders will vote on the bids made by the Albert Scardino-led group and a rival consortium led by Nigel Wray and local author Phil Soar.
The Anderson-backed proposal would see each of Forest's 202 shareholders receive around pounds 50,000 for their stake, far more than under each of the two other bids.
Last week, letters were sent to Forest shareholders by Phil Murdoch, a local antiques dealer who is also a shareholder, suggesting that they vote against both the Scardino and Wray-Soar bids.
However, Mr Anderson is thought to be unwilling to indulge in any spoiling tactics. He has made it clear that he will only re-enter the fray if neither of the two bids are successful next week.
Both Mr Reacher and Sandy Anderson were in the directors' box at Forest's FA cup defeat at Chesterfield on Saturday along with other well-known Forest fans including Chancellor of the Exchequer Kenneth Clarke.
The emergence of a third bid has been greeted with dismay by some Forest shareholders. They say further delays to the ownership question could jeopardise the club's future.
Forest's bankers are said to be ready to call in loans made to the club the day after next week's emergency meeting if neither of the bids is successful.
Larry Lloyd, a former Forest player and now a sports presenter on Radio Trent, said yesterday: "If this happens I fear for the club. I have spoken to some other shareholders and they feel the same."
It is understood that a shareholder buyout of Forest was discussed last autumn but dismissed on the grounds it was not financially viable.