Police are appealing for witnesses who saw a man being assaulted as he got on a bus in Rayleigh High Street this week.
The 20-year-old was hit on the head from behind as he boarded the First bus near The Factory Shop at about 1.50pm on Tuesday June 2.
Shortly before the incident, four men aged about 18 or 19, had approached him and were verbally aggressive.
They ran off down the High Street towards Crown Hill.
They were all described as white. One was about 6ft tall, with blonde slicked back hair. He was not wearing a top and had a tattoo on his chest.
Officers are continuing to carry out enquiries, including reviewing CCTV. Anyone who was in the area at the time and saw what happened, or has any information that could help with the police investigation is asked to call the Rayleigh local policing team on 101 quoting reference 42/79176/20.
Alternatively, contact the Crimestoppers charity anonymously on 0800 555 111 or use the anonymous online form at Crimestoppers-uk.org