At approximately 9.55am on Friday (9/10) a white Toyota Yaris and a bicycle were involved in a collision at the roundabout with Basingstoke Road and Whitley Woodway.
The driver of the vehicle stayed at the scene, but the cyclist, a 74-year-old man, suffered serious head injuries and was taken to the John Radcliffe Hospital in Oxford.
He remains in hospital at this time in a stable condition.
Investigating officer PC Jennifer Laurie, based at Three Mile Cross, said: “I’m appealing for anybody who witnessed this collision to please make contact with police.
“I’m particularly keen to hear from anybody who may have dash cam footage of the incident to get in touch.
“You can do so by calling 101, quoting reference number 43200317889″