While still regularly known as "Joe" at the time, Gantenhammer played collegiately at Long Island University.
He was taken early in the second round of the North American Soccer League draft with the 33rd overall pick by the Washington Diplomats.
[1] He played part of one indoor match for the Dips on February 12, 1978, making 13 saves in a 12–4 loss to Dallas.
[2] Gantenhammer did not make the Washington roster for the outdoor season, and instead settled in with the Pittsburgh Spirit of the Major Indoor Soccer League.
He played the 1984–1985 season with the Columbus Capitals in the American Indoor Soccer Association.