Club doctors told radio station Triple M at half time that it appeared to be a grade two medial ligament injury.
The 25-year-old twisted his right knee in a clinch with Magpie Luke Ball on the city wing of the ground about 20 minutes into the second term.
He crashed to the turf and was in considerable pain as he waited for the stretcher cart to arrive.
Schulz was taken from the field as the Power's substitute Cameron Hitchcock began to warm up on the bench.
The Magpies were 47 points up at the time of the injury and were yet to use their own substitute, late inclusion Brent Macaffer.
Macaffer came into the side for Leon Davis, who is ill with a cold.
