Three days after professional poker player Doyle Brunson launched a $700 million cash bid for WPT Enterprises Inc., the L.A.-based owner of the World Poker Tour television show said Monday it is unable to substantiate the credibility of the offer.

The uncertain news sent the firm’s stock plunging 11.6 percent to $23.43 in late afternoon trading Monday. The stock soared 49 percent when the offer was announced last Friday.

The company said that it received the unsolicited offer July 7 from Goodman and Chesnoff, a Las Vegas-based law firm, claiming to represent Brunson and a team of unidentified financial backers. WPT said that when it asked the law firm for more information after market close on Friday, it was told that the firm was no longer involved in the matter, the company said in a statement Monday.

WPTE said further attempts through the weekend to obtain more information were unsuccessful.

The offer expires on Tuesday at 5:30 p.m., with a one-week extension provision.

“While WPTE is not actively pursuing offers, it will seriously consider the merits of this or any other offer once it receives the requisite foundation information,” said Steven Lipscomb, WPTE’s president and CEO.

On Friday, Lipscomb said he did not think the offer was “reflective of the true value” of the company. Lipscomb said he would share the offer with the board of directors.

WPT Enterprises was founded in March 2002 and went public in August 2004 at $8 a share, raising $32 million.

World Poker Tour airs on the Travel Channel in the U.S. and in more than 60 markets worldwide.