In a Lillestrøm match against Ham Kam in June 1993, Grodås was injured before half time, and Knudsen made his senior debut.

At the time Grodås was injured Ham Kam was behind 0–2, but they eventually won 4–3 after four goals by Petter Belsvik.

He left Norway in 1999 for Danish team Ikast FS,[4] which in the same year was merged to form FC Midtjylland.

Already in January 2000 he left FC Midtjylland, after conceding eight goals in fifteen matches, for Stabæk in Norway, as a replacement for Frode Olsen.

[12] Knudsen made a bad performance against Odd Grenland and head coach Jörgen Lennartson chose Larsen as goalkeeper against Strømsgodset on 24 September.

[14] After playing the twelve first matches for Fredrikstad in the 2012 season, Knudsen lost the position as the first-choice goalkeeper to Jon Masalin.

[17] Knudsen was included in the national team squad for the first time in 2007, for a UEFA Euro 2008 qualifying match against Malta.

National team manager Åge Hareide was "impressed", although he was uncertain whether Knudsen would keep his first-team place on a long-term view.

[26] After he stepped down from professional football in 2012 he was employed as a goalkeeper coach at the Norwegian College of Elite Sport.