James Murray, 22, was found seriously injured after coming off his Carrera road bike on the B797 near Wanlockhead on Monday August 15.
Mr Murray, from Wanlockhead, was taken to the Queen Elizabeth University Hospital in Glasgow, where he died three days later.
No other vehicle was involved in the incident, which police were called to at around 7.40pm.
Officers have renewed their appeal for witnesses to come forward and are particularly keen to speak to the driver of a blue Peugeot.
Sergeant Leigh McCulloch, of Police Scotland, said: “We would like to speak to any witnesses who have not already contacted police.
“In particular we would like to speak to the driver of a blue Peugeot 306 or 307 which was seen travelling on this road towards Mennock around the time of the incident.
“Anyone with information is asked to contact road policing on 101.”