Police believe a cyclist found lying injured in a road in Borehamwood was assaulted.
The man was taken to hospital with serious injuries after being found late on Wednesday March 2 in Leeming Road.
Hertfordshire Constabulary says he suffered a bleed on the brain and he remains in hospital.
An appeal for information from the public was made earlier this month but following enquiries, the incident is now being treated by police as an assault rather than a collision.
Previous story: Cyclist found lying in Borehamwood street seriously injured
The emergency services were called to Leeming Road, by the roundabout with Gateshead Road, at around 11.50pm on March 2.
It had been reported a cyclist, who is in his 30s, was in the road. He was treated at the scene by paramedics before being taken to hospital.
Today, Detective Constable Ben Nash gave the following update: "The victim sustained serious injuries, including bleeding on the brain, and is still in hospital. This was initially being treated as a possible collision, but further enquiries and assessment of the victim’s injuries have led us to believe that this was an assault.
"We have launched a criminal investigation and are appealing for the public’s help in order to establish the exact circumstances surrounding this incident.
"We are appealing for anyone who was travelling in the area at the time, who witnessed either the incident itself or believe they may have witnessed a possible assault, to please get in contact.
"I would be especially keen to hear from you if you have a dashcam fitted to your vehicle. Please review the footage as a matter of urgency and send through anything you believe may be of significance."
DC Nash can be contacted at ben.nash@herts.police.uk or contact police on 101 quoting reference 41/18567/22.
Or contact Crimestoppers anonymously on 0800 555 111 or visit www.crimestoppers-uk.org.
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