On December 3, 2017, about 1530 eastern standard time, a Piper PA-34-200T, N8328V, was substantially damaged during landing at Thomasville Regional Airport (TVI), Thomasville, Georgia. The commercial pilot and three passengers were not injured. The airplane was registered to Quick Gas Aviation LLC and was operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Day, visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The flight originated at P K Airpark (5W4), Raeford, North Carolina about 1300, and was destined for TVI.The pilot reported that the enroute portion of the flight was uneventful. While lowering the landing gear for the approach at TVI, the left main gear did not indicate down and locked. The pilot cycled the landing gear three times, and then utilized the manual landing gear extension procedure, with no changes. Aerial observation of the landing gear by airport personnel indicated that all three-landing gear appeared to be down. The pilot continued the approach for a landing on runway 4. After touchdown, the left main gear collapsed. The airplane turned 90º to the left and came to a stop in the grass, adjacent to the runway. The airplane was examined by an airframe and powerplant mechanic with inspection authorization. Structural damage to the left wing was confirmed. The left main landing gear was found partially retracted in the gear well. The other gear were extended and locked. The airplane was raised with a backhoe and the left main gear was manually pulled down. The down lock hooks would not engage and the drag links would not allow full extension. The mechanic then ran his finger through the drag link mating surfaces and a small stone, with grease on it, came out and fell into the grass. He was unable to find the object in the grass. The landing gear then extended and locked in a normal manner. After manually troubleshooting the landing gear, hydraulic power was applied and the gear extended normally with three green indications. The airplane was then moved to a hangar where an additional examination was performed by a Federal Aviation Administration inspector who noted no anomalies.