Police are trying to solve the mystery of why no-one seemed to see an attack in a pub.
They have been trying to trace eye-witnesses since the assault at Broadfield Barton on Monday evening.
But no-one has so far come forward who witnessed the incident.
The victim, in his mid-30s, was drinking at about 8pm at the Imperial pub in the parade that serves part of the Broadfield estate Crawley.
A man beat the victim about the head, apparently without being provoked.
An ambulance crew took the badly-hurt man to East Surrey Hospital at Redhill.
He was at first suspected of suffering serious head injuries but has since been allowed home.
Detective Constable Ian Tremble of Crawley CID said he wanted any customers who saw went happened to come forward. He added: "The motive for the attack is not known."
The attack comes soon after police warned people in the same area to be careful after a recent spate of handbag snatches.
One elderly victim suffered a head injury but recovered despite suffering severe shock.
There have been at least four attacks and police believe they could be linked.
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