The 28-year old attacking midfielder was subbed out early in Hearts' 1-0 win over Hibernian on Sunday and Locke suggests there could be some serious ligament damage which would see him out of action for a large chunk of the campaign.
"I will probably find out more on Monday, it looks a bad one, maybe his medial ligaments," he said.
"It looks like I'm going to lose him for a number of weeks which is a huge blow because everybody knows we don't have the biggest of squads and he is a valuable player.
"He's getting a scan on Monday so we'll find out more then. It's not going to be great news whatever happens but I'm hoping he's not going to be out too long."