Three men were attacked by a gang armed with weapons near to a Doncaster canal.
The men were assaulted in Barnby Dun Road, Long Sandall, at around 11.30pm last night.
One of the victims was seriously injured, said South Yorkshire Police.
No arrests have yet been made.
A police spokeswoman said: "Police are investigating an incident that happened last night on Barnby Dun Road, Doncaster, at around 11.30pm.
"Police were called after three men were assaulted by a group of men who had weapons.
"One man was injured in the attack and was taken to hospital with serious injuries.
"At this time we do not have any descriptions of the attackers and no arrests have been made."
The area where the attack took place was cordoned off last night and remained in place this morning.
Witnesses or anyone with information should call South Yorkshire Police on 101.