The Icelandic international was left out of AZ's clash at Ajax on Sunday - which ended in a 6-1 demolition for Alkmaar - as he prepared to travel to England.
AZ boss Louis van Gaal explained why he left out Steinsson.
"Steinsson expects a transfer. Both clubs are in negotiations and there is a big chance there will be an agreement. Therefore I have placed Steinsson on the bench.
"I only want to work with players who are fully concentrated on AZ. That is with Gretar currently not an issue. He will probably leave the club."