The 23-year-old Iceland international winger has been with AZ since 2009, but he has decided not to sign a new deal at the AFAS Stadion.
Dutch clubs have to announce by April 1 whether they will renew deals of out-of-contract players, and AZ have confirmed that they will not be signing a new deal with Gudmundsson.
It is widely expected that Gudmundsson, who spent time with Fulham as a teenager, will be heading to England on a free transfer.
Previously, the likes of Bolton, Wigan and Nottingham Forest have been linked to the highly-rated wide-man.
Meanwhile, AZ have confirmed that Erik Falkenburg, Raymond Gyasi, Erik Heijblok and Paul Kok will also be leaving in the summer.