Officers were called to a section of A38 Alfreton Road at around 6.30am on Tuesday, March 29 after a collision involving a pedestrian.
The rider, a man in his 40s, suffered a serious head injury and is being treated in hospital.
A woman in her twenties was also injured and remains in hospital.
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The collision occurred on the westbound carriageway near Costa Coffee and Shell petrol stations.
Road closures were put in place for investigation work to be carried out and the incident caused heavy congestion on roads around Ashfield with Hucknall drivers affected as people tried to find alternative routes.
Officers would now like to speak to anyone who witnessed the incident.
Sergeant Craig Luckett, of Nottinghamshire’s Serious Collision Investigation Unit, said: “Two people were injured in this collision – one of them very seriously – and we are working to understand exactly what happened.
“Anyone who witnessed what happened and hasn’t already spoken to officers is asked to get in touch as soon as possible.
“We are especially keen to speak with anyone who may have dashcam footage of this incident.”
Anyone with information is asked to call Nottinghamshire Police on 101 quoting incident 72 of 29 March 2022.