The incident happened in Beacon Hill Country Park, Woodhouse Eaves, at around 5.40pm on Sunday 3 November.
The victim, 58, was assaulted when his dog ran up to a man in the park. The victim assured the man his dog was friendly but the suspect is reported as having launched himself, kicking and punching the victim who ended up on the ground.
He sustained a cut to the back of his head which didn’t require hospital treatment.
The suspect is described as white and around 5ft 9ins tall and of medium build with a bald head. He was wearing a beige coloured bomber jacket, jeans and beige shoes.
He verbally threatened the victim before walking away in the direction of the top of Beacon Hill.
PC Laura Hobbs is the investigating officer. She said: “The victim was left shaken and understandably shocked by his ordeal.
“We would like to speak to anyone who may have been in the area and witnessed either the incident itself or remembers seeing someone matching this description.
“Were you in the park at around this time? Did you see anything suspicious?”
Call 101 if you can help, quoting crime reference number 19*588998. You can also private message Leicestershire Police.