WEST Coast fears the worst for Eric Mackenzie’s season after the reigning best and fairest suffered a knee injury in the second term of the Eagles' NAB Challenge match against Carlton at Rushton Park in Mandurah.

Mackenzie was involved in a marking contest with Carlton's Levi Casboult on the wing. There appeared to be minimal contact between the pair but Mackenzie's right knee twisted slightly and he fell to ground in pain.

He remained on the ground as physios and trainers surrounded him.

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Mackenzie got to his feet and limped off without too much assistance and even broke into a jog as he neared the bench.

The physios conducted a stability test on his knee on the bench before Mackenzie limped to the rooms unassisted with two trainers.    

Eagles coach Adam Simpson said the club would know more after Mackenzie has scans on Saturday to assess the damage but he fears the defender has ruptured his anterior cruciate ligament.

"It's not great," Simpson said post-match.

"He left at half-time so I haven’t had a chance to talk to him but we fear the worst.

"You have your heart in your mouth when you go through these things and you just hope for the best.

"We all know he's an important player for us but we will park that for the moment and just get around him and see how he is tomorrow.

"We still don't know and there is still a small chance it might not be an ACL."

It soured a positive night for the Eagles. Simpson was pleased with his side's 31-point won over the Blues although he was a little frustrated by the Eagles' inaccuracy in front of goal. They kicked just 10 goals from 25 opportunities

"Unfortunately we didn't finish off our work and we had 25 scoring shots, but we came and did what we needed to do," Simpson said.

"Probably the most pleasing thing was that we were nice and organised and controlled with some of the things we went into the game with."

WATCH: Eric Mackenzie suffers a potentially serious knee injury against Carlton

Mackenzie's injury adds to some lingering concerns for West Coast. Jack Darling is unlikely to be available for round one, and possibly more games beyond that, as he continues his slow rehabilitation from a foot stress fracture.

Nic Naitanui was held out of the game against Carlton due to a back complaint and Simpson said he is no guarantee to return for the Eagles' next NAB Challenge against Port Adelaide at Norwood Oval on March 8.

"We're hoping, it'll be touch and go," Simpson said.

"We don't want to force the issue but we want to get some games (into him) as well. The pleasing thing that he's done is he's had a really good (run) during the pre-season. It's not like we're trying to cram in some work. He's done a lot of minutes, so now it's probably getting match fit."

Scott Selwood returned to the training track this week following ankle surgery in December. He appears to be pushing to play in one of the next two NAB Challenge matches but Simpson said they would not rush him back.

"We're just going to take that one pretty slow," Simpson said.

"He trained this week.

"If we can get him through another week of training and he might sneak in a last NAB Challenge match, but we're pretty patient with his return."