ADELAIDE coach Matthew Nicks says mystery remains on the replacement for key defender Nick Murray for a clash against a St Kilda side without Max King.

Murray, described by Nicks as the rock of Adelaide's backline, will miss Sunday's Adelaide Oval fixture because of concussion.

St Kilda has ruled out a return for tall forward King as he recovers from pre-season shoulder reconstruction.

"We feel another week of full training will better set him up to perform potentially next week," the Saints' acting football manager David Misson said.

"He's put in a lot of hard work over the summer to get back so we're not going to be impatient this week."

The King call leaves Nicks uncertain whether he will summon another tall defender as a like-for-like replacement for Murray.

Nicks has ruled out young backman Josh Worrell due to limited game time in state league ranks.

"We haven't locked it in, it's quite a big decision for us, that one," Nicks told reporters on Thursday.

Irishman Mark Keane is in the selection frame for a debut for the Crows but didn't play in state league last weekend because of a neck injury.

Nicks said smaller backmen such as Patrick Parnell, Will Hamill, Andrew McPherson and Luke Nankvervis, who is yet to play an AFL game, were also in the discussion.

"A number of guys are knocking on the door ... (it's) really pleasing to have that availability for guys to come in," Nicks said.

"We will just have a number of things ready depending on the opposition but we will also play what we feel is our best side."

Adelaide has dropped to 10th place following consecutive losses to Collingwood and Geelong ahead of hosting the third-placed Saints.

"We have played two very good sides that don't allow you to do certain things with the game and we have been challenged with that," Nicks said.

"We have still got to improve to match those sides consistently.

"But we're playing good footy."