Whether it be the footballing gods paying West Coast back for past misdemeanours, or just plain bad luck, the Eagles have lost another top-line midfielder just when they needed him most.

Already struggling to replace the influence of Ben Cousins and Chris Judd, the Eagles engine room will have do without Matt Priddis for at least three weeks after he had to undergo knee surgery.

More than the usual soreness after Saturday's western derby loss to Fremantle prompted the club to order scans, which revealed detritus in Priddis' left knee which needed immediate attention.

"After having scans done he needs some surgery done. He is in today and I think he might have had it done. He looks like missing a minimum of three weeks," coach John Worsfold said.

"It is not a medial, it's floating bone. He has torn off a little bit of bone, so they have had to go in and suck that out.

"It happened during the game and he got through the game, but he pulled up pretty sore the next day and then sorer the next day."

Priddis' first three games in 2008 have seen him take over as one of the Eagles key on-ballers.

He's found the ball 86 times, two more than even star on-baller Daniel Kerr, and just eight behind the competition leader Joel Corey.

With Priddis also executing 18 clearances - one behind Kerr who tops the AFL in that list - the absence of the 23 year-old will be hugely felt against the Swans.

Add to that the huge doubts over ruckman Dean Cox, and Saturday's clash with Sydney at ANZ Stadium looms as a daunting prospect.

Cox hurt his right foot in the first quarter against Fremantle, and while x-rays and scans cleared him of major damage, Worsfold said Cox would need to be "better than 50-50" before the club would even consider taking him east.

"He is still very confident he will be right to play and I don't think we'll travel him to Sydney if he is only 50-50," Worsfold said.

"I think he will want to be a lot more than that for us to take him over there to see if he comes up. Really, tonight's training will be the biggest test for us.

"If playing with it was going to make it worse, or make him carry it for a longer period, then the advice would be you are probably better off resting him and letting him get over it.

While it would not seem West Coast's week could not get any worse, Worsfold said he was confident his team would be able to solve their problems with turnovers and skill errors.

"There is a couple of glaring things that aren't working that well for us that most people are aware of. We are going to address those. But we are not far away," Worsfold said.

"We need to improve, because there is no use being within a kick of sides halfway through the last quarter and still losing, but we know where that improvement can come from and we are confident we can deliver on that."

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