According to the certificated flight instructor (CFI), the purpose of the flight was for the student pilot to perform a night cross-country. After completing a full stop landing at the destination airport, they taxied back to the runway to complete additional practice of flying in the traffic pattern. While on the takeoff roll, as the student pilot began to rotate the airplane airborne, the CFI observed an animal directly in front of the airplane on the centerline. He took authority of the flight controls in an attempt to not collide with the animal as the airplane began the initial climb. He heard a "bang" as the airplane passed over what was later identified as a deer. The CFI then noticed the left rudder pedal was looser than normal and no brake pressure was observed in the left toe brake. After a few low passes and confirmation from the control tower personnel that the left landing gear was not in the normal position, the CFI decided to land the airplane. During landing rollout, the left wing struck the ground and the airplane came to rest on the runway. The postaccident examination by a Federal Aviation Administration inspector revealed that the left landing gear had separated, resulting in substantial damage to the left wing spar. According to the CFI, no mechanical anomalies were present prior to hitting the deer.