The student pilot stated that the airplane’s left main tire felt flat during his third solo landing. After landing he taxied back to the fixed base operator (FBO) to have the tire checked. The FBO representative did not note any discrepancy, and the pilot taxied back to the runway to continue the flight training. During takeoff, as the airplane reached about 30 knots, the airplane began to bobble on the left side so the pilot reduced power back to idle and applied the brakes. The airplane continued toward the left off the runway, and came to a stop in a ditch,, incurring substantial damage to the firewall. The responding Federal Aviation Administration inspector stated that the left wheel assembly did not reveal discrepancies that would have prevented normal operation of the assembly.