Paul Hasleby ruptures his medial ligament of his left knee in Fremantle's win over West Coast during the pre-season.

Hasleby will have scans to determine the extent of the damage and whether a reconstruction will be required.

"At this stage, it is a medial ligament but we aren't totally sure until after he has a scan. That is significant in itself, but we have our fingers crossed that that's all it is," Dockers coach Mark Harvey said.

"When a guy like Hase has put everything on the line, the last thing you want him doing is missing the whole season. That was the only downside to the game for us."