DALLAS ( TheStreet) -- Blockbuster ( BBI), the video rental chain, said it could be forced to file for bankruptcy if cash flows don't improve and it's unable to restructure its debt. Blockbuster's debt load has been reported to be as high as $1 billion. "These factors raise substantial doubt about our ability to continue as a going concern," Blockbuster said in a filing with the Securities and Exchange Commission. Blockbuster said "increasingly competitive industry" conditions have hurt its operations. Blockbuster reported a fourth-quarter loss of $434.9 million, or $2.24 a share, as same-store sales fell almost 16%. Competitors such as Netflix ( NFLX) and Redbox have taken market share. Blockbuster shares fell Tuesday by 2 cents, or 4.1%, to 40 cents. -- Reported by Joseph Woelfel in New York. Follow TheStreet.com on Twitter and become a fan on Facebook.