At around 3am today, a 34-year-old man left a property in Binfield Road in Bracknell on a white electric scooter with black handles.
The man was then found by a friend at approximately 3.30am, with a serious head injury in the Twin Bridges Roundabout underpass.
The ambulance service was called and the man was taken to the Royal Berkshire Hospital, where he remains in a serious condition.
Detective Inspector Richard Johnson said: “I am making an urgent appeal to anyone who was in the centre of Bracknell, especially the route between Binfield Road and the Twin Bridges Roundabout.
“If you have any footage from this area of Bracknell in the early hours of this morning, whether on your phone, dashcam, doorbell or any other device, please contact the force.
“I am also keen to hear from anyone who believes they saw the man or may know how he sustained this serious head injury, to please come forward.
“The easiest way to contact the force is online or call 101, quoting investigation reference number 448 (25/4).
“There is a police cordon in place at the Twin Bridges Roundabout underpass, which is likely to remain in place for the foreseeable future. I apologise for the inconvenience that this closure will cause to local residents, however the force needs to carry out vital enquiries at the scene.
“We are keeping an open mind as to how the man sustained a serious head injury, but I want to reassure the community that a thorough investigation is being carried out to establish what happened.”