Leighton, who was on the club's board during the era of former chairman Peter Ridsdale, always maintained after his departure from Elland Road that he would assist with any credible takeover bid.
He has been attracted by the commitment of Stubbs, and is believed to have pledged £2m, though his contribution may reach £5m.
More than £12m is currently available to Stubbs, who met representatives of the Leeds board yesterday to discuss his offer.
Leeds are still around £25m in debt and owe around £3.5m to the Inland Revenue, which is pressing for payment following previous defaults.