Shares of Red Robin Grourmet Burgers Inc. ran up 27% in active premarket trade Thursday, after the restaurant chain disclosed that its third-largest shareholder, Vintage Capital Management LLC, said it was prepared to make a buyout bid for the company. In a letter Red Robin's board of directors, Vintage, which owns 1.5 million shares, or 11.5%, of Red Robin's outstanding shares, said it was prepared to pay $40 a share in cash an auction to buy the rest of Red Robin shares that it didn't already own. That would represent a 57% premium to the stock's Wednesday closing price, and would value the company at about $519 million. Earlier this month, Red Robin adopted a shareholder rights plan, known as a poison pill, aimed at protecting the company from a hostile takeover. Vintage said it has sought communication with management to help drive an improvement in the strategic direction and to help recruit "an 'A+' operator" to accept the chief executive officer role, given that "it is clear that many such quality candidates are refusing to entertain the opportunity due to the lack of confidence in the board's leadership and Red Robin's disastrous operating and market performance." Red Robin's stock has tumbled 52% over the past 12 months, while the S&P 500 has gained 3.8%.