Microsoft, Silverlake and TPG Capital were all signatories with Yahoo, unnamed sources close to the situation told the New York Times.
The interested firms will now have a closer look at Yahoo’s books, the publication reported.
Microsoft has reportedly examined an option in which it would contribute billions of dollars to an acquisition alongside the private equity firms.
The Windows firm tried three years ago to buy Yahoo, seeing it as a key competitor to Google and putting up some $45 billion. But Yahoo turned down the offer.
Microsoft chief executive Steve Ballmer said last month that he felt “lucky” that Microsoft did not make the 2008 aquisition.
While Ballmer clarified the statement by saying that such an acquisition would have happened around the collapse of Lehman Brothers, market observers have speculated that Yahoo could come back with a lower offer this time.
Yahoo, which fired its last chief executive Carol Bartz in September following a tough few years at the company, has an important search and advertising partnership with Microsoft.
It remains unclear whether an acquisition will materialise. Microsoft and Yahoo have declined to comment.