[4] Following a poor second season and Champions League campaign from Sydney FC, Keller was released along with several other players.

[5] Keller returned to Europe and sparked interest from former Eredivise club RKC Waalwijk.

[6][7] However, in a shock move Willem II signed Keller on a two-year contract, snatching him from under the nose of his former employee.

Patrick Rahmen was installed as new manager the following season and Keller stayed with the club as his assistant.

[10] On 1 November 2022, after a six game winless streak in the league, he was dismissed from his position as head coach at Aarau.