Police are appealing for witnesses after a man was left critically ill in hospital following a street attack.
His life has since been saved by surgeons at Hurstwood Park Neuroiloigcal Unit in Haywards Heath.
Sussex Police say the victim was rushed to Hurstwood Park on September 13 when doctors realised he had a life-threatening brain injury.
He underwent emergency brain surgery from which he is currently recovering.
Det Con Karrie Bohanna said: “This was a nasty unprovoked attack that could have proved fatal.
“If the victim had not been with his family when his condition worsened he might not have got the treatment he needed in time.
The 53-year-old was attacked by a group of three men outside Energie fitness club in London Road, East Grinstead in the early hours of Sunday July 28 but did not realise how seriously injured he was for more than a month.
He was punched in the face and hit on the back of the head between 1am and 2am before being helped by people in the area to get home.
Sussex Police say the victim did not report the incident as he did not know how badly he was hurt.
While abroad on holiday in August he suffered headaches and sickness which worsened until he could not recognise friends and family.
After returning home he was sent for a scan and was then rushed to Hurstwood Park where specialists diagnosed his brain injury.
Police now know that the victim’s attackers had been sitting on a bench with a woman outside Energie before the attack took place. All are described as white and in their early twenties.
DC Bohanna said: “I am keen to speak to anyone who saw the attack taking place or the victim being helped in the moments afterwards.
“As the victim did not appear too seriously hurt after the assault, anyone who saw what happened may not have come forward yet but I would urge them to do so.
“Also, if you were one of the men involved in the attack I would urge you to contact us.
“You may not have realised how badly injured the victim was but we need to speak to you.”
Anyone with information should call 101 quoting serial 490 of 18 September or the independent charity Crimestoppers anonymously on 0800 555111.