Three teenagers were taken to hospital after being attacked in the park in Salford.
It happened in Buile Hill Park, off Eccles Old Road, shortly before 3pm on Monday, December 28.
Police say they were called at 2:50pm by paramedics responding to a reports of two people being injured.
Officers attended and established that an 18 year-old man and two teenage boys, aged 17 and 14, had been assaulted.
All three were taken to hospital.
Passers-by reported seeing an area around an entrance to the park on Eccles Old Road adjacent to Manor Road taped off for several hours on Monday afternoon.
Their injuries are not believed to be serious and they are expected to make a full recovery, Greater Manchester Police (GMP) said in a statement this morning.
An investigation was also underway to identify the culprit they added.
They are asking for anyone who may be able to help them in their enquiries to come forward as a matter of urgency.
Detective Sergeant Roger Jones, from GMP's Salford division said: "Thankfully the victims weren't seriously injured.
"Nevertheless, enquiries are ongoing to identify the person responsible.
"We know that there were a number of people in the park at the time so I would appeal to them to contact us or Crimestoppers, anonymously.
"I would also encourage anyone else with information which may assist us with our enquiries to do the same."
Anyone with information should contact police on 0161 856 2079 quoting 1474 28/12/20 or Crimestoppers, anonymously, on 0800 555 111.
