The rider was travelling along Grane Road when he turned left onto Holcombe Road at around 4pm on Wednesday (June 16).
Shortly afterwards, he left the road before crashing into a lamp post after losing control of his bike.
The motorcyclist, a 35-year-old man from Haslingden, suffered serious head and chest injuries and was taken to Royal Preston Hospital by air ambulance.
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He remains in a serious but stable condition and his family have been informed, police said.
Sgt Phil Baxendale from Lancashire Police's Tactical Operations said: "We need anyone who was in the area and saw what happened or who may have seen the motorcyclist prior to the collision, to speak to us as they may have important information to assist our investigation."
Anyone with information has been asked to call 101 or email [email protected] quoting incident reference number 1020 of June 16.
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