Askou played 27 times in Norwich's 2009/10 League One promotion term
Norwich City have not offered new deals to Jens Berthel Askou, Matt Gill and Sam Habergham and all three have left the club.
Centre-half Askou, 28, and 30-year-old midfielder Gill arrived at Carrow Road in the summer of 2009.
Defender Habergham, 19, failed to play a first team game after signing professional terms two years ago.
"Gilly is a great pro and for his own career he has to go and play," boss Paul Lambert told BBC Radio Norfolk.
"Same as Jens, he was never a problem, but they have to go and play football.
"Sometimes when you lose people, especially like Gilly, it's a sore one."
Norwich-born Gill played only 16 times in his two years at the club, spending an eight-game loan spell with Walsall in early 2011.
Dane Askou will return to his homeland in search of a new club after making 33 appearances during his 24 months in Norfolk.
He had a disappointing loan stint with Millwall in January which saw him sent off in his only appearance.
