Police were called after a brawl broke out in Central Drive at around 5.30pm on Saturday (June 25).
A man in his 20s was found with a “serious head injury” when officers attended.
He has been taken to the Royal Preston Hospital where police said he remained in a “serious but stable condition”.
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A man and two women were also punched and kicked during the altercation, police said.
On Monday (June 27), detectives released CCTV images of two people they wanted to speak to in connection with the attack.
Det Insp Steve Montgomery, of Blackpool Police, said “This happened on a busy street in the middle of the day where there were lots of people and traffic around.
“I believe that the man and woman in these images may be able to assist in our enquiries.
“I would appeal for anyone who saw what happened or anyone with dashcam footage of the incident to come forward.”
If you recognise the people in the images or have any information which may help police, call 101 quoting 1127 of the June 25.
Independent charity Crimestoppers can also be contacted anonymously on 0800 555 111.