Aman in his 20s is in hospital with a stab wound and police are looking for another man they believe may also have been injured in the same incident.
Witnesses reported seeing two injured men in Penistone Road North, Hillsborough, at around 7.20am today.
Only one has currently been traced.
A South Yorkshire Police spokeswoman said: “The second man is yet to be traced and officers are keen to locate him as he may require medical attention for his injuries.
“He was last seen walking along Penistone Road North and in the Hillsborough Park area.”
Anyone with information should call South Yorkshire Police on 101 or Crimestoppers on 0800 555111.