WEST Coast star Josh Kennedy is facing an uncertain stint on the sidelines after hearing a pop when he went down with a suspected calf injury in Sunday's loss to Greater Western Sydney.

The Eagles spearhead collapsed early in the final term when he tried to change direction in the forward line, only moments after steering through his third goal to put West Coast in front.

Coach Adam Simpson said post-match that Kennedy heard a pop when he went down, but declared "that happens a lot when you hurt your calf".

Kennedy was carried from the field in obvious pain and had ice strapped to the back of his lower right leg as he watched the rest of the match from the bench.

In the aftermath of the eight-point defeat, Simpson was in the dark about how long Kennedy would be out of action.

"I'm not quite sure, he's hurt his calf so I'm assuming he won't be back before the bye (after next weekend's clash with Gold Coast)," Simpson said.

"The feedback we're getting is it's a calf. I think he was a little bit worried there early on (that he hurt his Achilles), but I think it's probably calf.

"Sometimes they hurt. He heard a pop. The diagnosis at the moment is it's a calf, but it's early on so we'll see how he pulls up.

"Of course I am hopeful that's the case (that it's not too serious)."

McGovern likely to fill Kennedy hole: Simmo

Losing the focal point of their forward line – and their most important player in the absence of ruckman Nic Naitanui - for an extended period of time would be a major blow for the Eagles.

Kennedy has played 103 of the past 106 games and has returned hauls of 80 and 82 goals in the past two seasons to win back-to-back Coleman Medals.