Officers say two men were found with head and facial injuries in Newton Street, Deepdale at around 10.20pm on Thursday after a member of the public reported a disturbance to police.
It is believed the injured men got into an altercation on Meadow Street before they have made their way to Newton Street where they were found.
Both victims, aged 30 and 34, suffered facial injuries and were taken by ambulance to the Royal Preston Hospital for treatment.
Two men aged 34 and 29, from Preston, were later arrested on suspicion of assault. Both have since been released on bail pending further police enquiries.
DS Jerry Sturgess said: “We believe that there may have been an altercation between these four males in the Meadow Street area before they have ended up in Newton Street.
“We would urge anyone who saw the four man arguing or has any information that could assist with our enquiries to come forward.”
Anyone with information about the incident can contact police on 101 quoting log reference 1613 of April 6.
Alternatively, they can contact Crimestoppers anonymously on 0800 555 111 or online at Crimestoppers-uk.org.