Officers were called to the park at just after 18:20 GMT on Sunday
Two men were stabbed in a Wolverhampton park after confronting robbers.
The men were sitting with a group of people in West Park when they were approached by four men who took a bike, West Midlands Police said.
The force said the victims were threatened and stabbed after chasing the men.
One man aged 34 was taken to hospital where his condition is described as stable. The other man, aged 33, was treated for minor injuries.
The robbers were described as black and in their late teens. It is believed they were wearing dark clothing, police said.
Officers were called to the park at just after 18:20 GMT.
Insp Phil Asquith said: "We are eager to speak to anyone who was in the area of the park yesterday afternoon.
"This was a particularly vicious attack."