 Fitness problems blighted Thelwell's time at Hull City, and he missed over a year from October 2004 to February 2006 due to a serious knee injury.He signed a new short-term contract in January 2006, and after proving his fitness and featuring in nine of City's last thirteen games of the 2005–06 season, Thelwell was rewarded with a further year's contract extension.Finding his first team opportunities at the KC Stadium limited, he joined Leyton Orient on loan in October 2006, making his debut in the League One fixture against Cheltenham Town on 21 October 2006, Orient winning 2–0.