Iain Dowie is said to be ready to pay £1.5million plus the Dane, a bid that City boss Nigel Worthington would see as preferable to a mooted £2million offer from Alan Pardew's West Ham.
Andersen, 24, has played 18 times for Charlton and made his only international appearance for Denmark in a 2-0 defeat against Spain in 2004. He played 60 times for AB Copenhagen before moving to the Valley just over two years ago.