Officers say it happened on Tuesday around 5:30 near the 1200 block of Oneida St.
Menasha Police say vehicle was driving north when it hit the bicyclist, and then left the scene. The 25-year-old male victim, from Appleton was taken to the hospital for a severe concussion.
Police say they don't have any information on the striking vehicle, but there may be front end damage.
If you have any information, you should call Menasha Police at (920) 967-3500.