George Warren Grebenstein (September 19, 1884 – May 21, 1980) was an All-American basketball player at Dartmouth College as a junior in 1905–06. A forward, he was the first Dartmouth player to be named an All-American while leading the Big Green to a 16–2 record. The Helms Athletic Foundation retroactively named Dartmouth the national champion that season since it occurred prior to the NCAA tournament. He graduated from Dartmouth in 1907. Grebenstein went on to coach the Harvard men's basketball team in 1907–08 and 1908–09. He compiled a record of 5–19.