Emergency services were called after a man was found unconscious in North Street, Brighton, at around 7.10am.
He was taken to hospital where he remains in a critical condition.
A large police cordon which was in place on a section of the pavement by North Street has been removed.
A 28-year-old man of no fixed address has been arrested on suspicion of robbery and remains in police custody.
A 43-year-old woman from Brighton has been arrested on suspicion of robbery and remains in police custody.
A 30-year-old man has been arrested on suspicion of GBH and remains in police custody.
Detective Chief Inspector Miles Ockwell said: “We would like to speak with anyone who was in the area at the time of the incident and who may have seen what happened.
“I would like to thank anyone affected by the cordon for their patience whilst our investigation continues, our Crime Scene Examiners will be working to re-open the footpath as soon as possible.”
Witnesses can email [email protected] call 101 quoting serial 317 of 23/01.
Alternatively, you can call the independent charity Crimestoppers anonymously on 0800 555 111 (www.crimestoppers-uk.org).
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