General aviation student pilot reported a brake malfunction which resulted in a rejected takeoff and runway excursion into a gravel area. The pilot did not report any damage to the aircraft; airport or injuries.

Narrative

During the power-up to takeoff at around 40+ knots; I felt as if the right rudder pedal was stuck or obstructed; preventing full range of motion. The pedal lacked a positive feel; and it seemed as though the right brake might have been locking or dragging. This sensation was very different from how the aircraft had felt during previous takeoffs. With only seconds to react before committing to takeoff; I ensured my heels were on the floor and not depressing the brakes. I immediately reduced power and gently applied the brakes to slow the aircraft. As the aircraft began to brake; it quickly veered left; despite my certainty that I was not pressing the left rudder pedal or applying the left toe brake only. The aircraft continued to veer left; heading toward the left side of the runway. I tried to brake just enough to avoid locking the brakes or over-braking; which could cause the aircraft to flip. However; the braking force needed to prevent further complications was insufficient to stop the aircraft on the runway; leading to an excursion into the gravel area on the left side. While continuing to apply gentle pressure; I managed to stop the aircraft in the gravel; experiencing a slight spinout but avoiding a prop strike or flip-over incident.