The attempted sexual assault at 362 W. El Norte Parkway was reported at 10:10 p.m. Tuesday, according to Escondido police Sgt. Eric Distel.
The man apparently hid in a children's play area inside the gym and attempted to attack the woman while she was alone, Distel said, adding that the woman thwarted the attack but sustained minor cuts and abrasions in the process.
She was taken to Palomar Medical Center to be evaluated, he said.
Police were looking for a heavyset Hispanic man in his 40s with a shaved head and tattoos on his left-hand knuckles. He may also have a tattoo near his left eye, possibly of a tear drop, Distel said.