The incident happened around 7pm on Saturday, March 20, at Douglas Park.
A 38-year-old man was taken to Forth Valley Royal Hospital after sustaining serious head injuries.
He had been struck with a weapon.
Police Constable Kendall Brown, of Grangemouth Police Station, said: “We are appealing for information from members of the public to help trace those involved.
“The area would have been busy with people at the time and we would encourage anyone with any information to come forward and speak to police.
“If anyone has any information about posts on social media relating to the assault that could assist our enquiries, I would ask that you get in touch with officers.
“Anyone with any information is asked to contact police on 101 quoting incident number 0798 of 29 March.”