A man fell onto train tracks after being punched in the face on a railway station platform.
The incident happened at Coatbridge Sunnyside Station in North Lanarkshire at 2.35pm on Thursday, April 11.
British Transport Police, who are now appealing for witnesses, said the victim had been arguing with his attacker before being assaulted.
A spokeswoman said the man suffered a serious head injury after hitting the tracks.
His assailant is described as a white 16-year-old, with a slim build and short dark hair.
He was wearing a black hooded jacket, grey jogging bottoms and black trainers at the time of the attack. Officers are urging any witnesses to get in touch.
They also want to speak to two women who were with the suspect at the time of the attack.
Anyone with information can contact BTP on 0800 40 50 40 or via text on 61016.