A cyclist collided with a parked Vauxhall Corsa in Manxman Road at around 4.15pm on Sunday (May 15).
The cyclist – a man in his 30s – was thrown from the bike, resulting in him suffering “serious head injuries”.
He was taken to Royal Preston Hospital for treatment.
Sgt Peter Snook, of Lancashire Police’s Tactical Operations, said: “An investigation is underway after a cyclist was left with serious injuries following a collision in Blackburn.
“We have spoken to a number of witnesses but would ask anyone who saw what happened and has yet to speak to police, to come forward.”
Anyone with information can contact the police by calling 101 or email [email protected], quoting log number 1167 of May 15.