TechCrunch cited in house documents that were leaked. Microsoft did not respond to a request for a comment and Barnes & Noble declined to speak on the speculation, CNNMoney.com reported Thursday.
Barnes & Noble shares, however, jumped 16 percent in early trading after word got out that Nook might have a buyer.
Microsoft already owns 18 percent of the business, which it bought for $300 million in April 2012.
Barnes and Noble has also said it was considering spinning off its digital reader and e-book business.
That was in early 2012. Early this year, Leonard Riggio, the chairman of Barnes & Noble and its largest shareholder unveiled a plan in which he would buy the retailer's stores and spin off the Nook at the same time.
Barnes & Noble has upgraded the Nook hardware, releasing an HD -- or high definition -- model in September. But Barnes & Noble is still struggling to keep up with Amazon, which has a vast audience as a retailer and produces the highly successful Kindle e-reader.
TechCrunch reported that Nook plans to drop the hardware end of its business within two years and make e-books available through applications on other devices.