Due to an injury picked up in the pre-season match against Nottingham Forest, Sullivan made few appearances in the 2006–07 campaign for Leeds, with loan goalkeeper Tony Warner filling in whilst Sullivan was injured. Kevin Blackwell was sacked and replaced by Dennis Wise. Wise decided to sign Graham Stack on loan to compete with Warner and Sullivan. On 23 November 2006, he moved on loan to Doncaster Rovers. His loan was however cut short and he returned to Leeds on 21 December 2006. Manager Dennis Wise told the press after Leeds' 2–1 victory against Coventry City that Sullivan had put on weight, and his performances were not as good, hence his loan to Doncaster. Leeds signed Casper Ankergren as the new number one goalkeeper. Sullivan re-signed on loan for Doncaster Rovers in February 2007. After the end of his loan at Doncaster, Sullivan returned to Leeds but was released at the end of his contract.