NFL-Patriots cut Tebow, who vows to fight on for pro job

* Quarterback's NFL future in doubt * His popularity goes beyond U.S. football (Updates with confirmation and Tebow quote) By Simon Evans NORTON, Massachusetts, Aug 31 (Reuters) - The New England Patriots cut quarterback Tim Tebow from their roster on Saturday throwing serious doubt over the former college star's future in the professional game. Tebow, joined the Patriots this off-season after he was released by the New York Jets where he spent last year as a rarely used back-up to Mark Sanchez. A former Heisman Trophy winner and two-time national champion with the University of Florida, Tebow has a strong personal following among fans but has struggled to transform his success at the college level into the pro game. The 26-year-old always faced a tough task to make the roster with New England who have future Hall of Famer Tom Brady as starting quarterback and Ryan Mallett as back-up. But after hearing the news, Tebow took to Twitter to thank the Patriots for his chance and express his determination to continue in the NFL. "I would like to thank (Patriots owner Robert) Kraft, Coach (Bill) Belichick, Coach (Josh) McDaniels and the entire Patriots organization for giving me the opportunity to be a part of such a classy organization," wrote Tebow. "I pray for nothing but the best for you all. I will remain in relentless pursuit of continuing my lifelong dream of being an NFL quarterback," he added. Tebow was drafted by the Denver Broncos in 2010 and in his second year took the Broncos on an improbable run to the playoffs, beating the Pittsburgh Steelers before losing to the Patriots. He also quickly become a major celebrity, with his popularity going well beyond the NFL. Deeply religious and with a clean-cut image, he became a magnet for sponsors, signing a range of massive endorsement deals which earned him an estimated $4 million a year. Tebow's jerseys were among the biggest sellers in the NFL and his habit of going down on one knee in prayer became known as "Tebowing." In early 2012, the Broncos signed quarterback Peyton Manning after he had become a free agent and traded Tebow to the Jets. (Reporting By Simon Evans, editing by Alan Baldwin and Gene Cherry)