Man found seriously injured in Sydney park

A crime scene has been set up after a young man was found seriously injured in a Sydney park.

The man, believed to be in his 20s, was discovered by a woman out on her morning walk at Greenacre Heights Reserve, in Sydney's southwest, about 6am on Wednesday.

Police are yet to identify the man, who has been taken to hospital in a serious condition.

He is expected to undergo emergency surgery but his injuries are not considered life threatening.