Barnes & Noble Inc reported a deeper-than-expected quarterly loss on Tuesday as the largest U.S. bookstore chain came under pressure from the going-out-of-business sales of bankrupt rival Borders Group Inc.

Barnes & Noble said sales at its namesake superstores open at least 15 months fell 2.9 percent during the quarter, hurt by the liquidation of 200 bookstores by Borders .

The weak results come as Barnes & Noble, which put itself up for sale last summer, is evaluating last month's $1 billion bid by John Malone's Liberty Media Corp .

Barnes & Noble shares, which have more than doubled since April, were up 0.7 percent at $20.27 in morning trading. The stock has been trading above Liberty's $17 offer since the bid was made, suggesting investors believe another suitor may step in.

Morningstar analyst Pete Wahlstrom said Barnes & Noble shares were modestly overvalued because of uncertainty surrounding book sales, which still make most of the company's business, and stiff competition in the e-books industry. He also expressed doubts that another bidder would emerge.

Digital is growing nicely, but probably not enough to materially change how third parties are thinking about the overall business (at this point) and incent them to come in and bid, Wahlstrom said.

Citing the Liberty bid, the company said it would not provide a sales or profit forecast for the second quarter in a row.

The Borders closings and investments in Barnes & Noble's Nook e-reader took a bigger toll on results than Wall Street analysts expected.

Barnes & Noble introduced the Nook in 2009 to compete with Inc and its market-leading Kindle. But the investment is expensive. In February, the chain suspended its dividend to conserve money for the Nook.

The Nook has been successful, becoming the second-best selling e-reader. During the quarter, Barnes & Noble introduced an improved version of its Nook Color tablet to better compete with Apple Corp's iPad. It also began selling a touchscreen Nook.

Barnes & Noble said its loss had nearly doubled to $59.4 million, or $1.04 per share, in the fourth quarter ended April 30, from $32 million, or 58 cents a share, a year earlier.

That was worse than the loss of 91 cents per share that analysts were expecting, according to Thomson Reuters I/B/E/S and brought the full-year loss to $73.9 million.

Online sales, helped by Nook, rose 78 percent, while same-store sales at the College bookstore chain rose 3.5 percent. Each unit accounts for about one-sixth of sales. Overall quarterly sales were up 4 percent at $1.37 billion.

Barnes & Noble, which operates 717 superstores, said its sales had risen in markets where Borders stores have closed.

(Reporting by Phil Wahba, editing by Gerald E. McCormick, Maureen Bavdek and Lisa Von Ahn)