Knight spent 22 years playing at Fratton Park, making 801 appearances between 1978 and 2000 – the record for a keeper at a single English club. He kept a clean sheet on his debut, aged 16, against Rotherham in the old Division Three in 1978 and went on to represent the club in all four divisions. Knight was awarded an MBE following his retirement, and was also handed the Freedom of the City of Portsmouth.
Knight's final appearance for the club came aged 38 on 3 January 2000 in a 2-1 Division One defeat at Norwich, making him the only Blues player to have played across four decades. Speaking to the BBC following his cancer diagnosis, Knight said it "came as a massive shock" but he wanted to discuss it publicly to encourage others to seek advice if they spot symptoms. He joined a group of men playing walking football in Portsmouth and said it helped them all come to terms with their diagnoses.
Knight's legacy at Portsmouth is still celebrated by fans, who gave him the nickname 'The Legend'. He was a key player in three promotion-winning campaigns, including a Division Three title success and Pompey's return to top-flight football for the first time in 28 years in the 1986-87 season.