Police confirmed the incident occurred at approximately 8pm on Friday, June 27, with the cyclist suffering serious injuries in Portsmouth Road.
Hampshire Constabulary confirmed the 29-year-old man is being treated in hospital for “life threatening injuries,” with officers still conducting their investigation.
READ MORE: Portsmouth Road reopens after police close road due to crash
It comes after Portsmouth Road was closed by police last night between the Station Road junction and the Itchen Bridge roundabout.
Police confirmed the road had reopened this morning.
In a statement, a spokesperson for the force said: “Officers would like to speak to anyone who saw what happened or anyone who may have dashcam footage of the incident.
“Please contact us online or on 101 quoting 44250284830.”