Ambulance crews called police after they discovered a man had been stabbed in the leg in Cotton Hall Street at around 4.30am today (June 30).
The victim, a man in his 40s, was taken to the Royal Preston Hospital where officers said he remains in a "serious but stable condition".
Detectives reviewing CCTV footage as part of their enquiries now believe there may have been another stabbing just 15 minutes earlier.
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The footage appears to show a man - who is in company with another male - being stabbed in the lower back by an assailant at the rear of Heyfold Gardens, police said.
No victim has come forward in relation to the incident and officers are appealing for them to get in touch so they can check on their welfare.
Det Insp John McNamara, of East CID, said: "During our enquiries we have found some footage which appears to show another, earlier assault.
"So far no victim has come forward in relation to that and I would appeal for them to come forward if they are able to, or for anyone who has information about either incident to get in touch."
Enquiries are ongoing and a 15-year-old boy was arrested on suspicion of Section 18 wounding this afternoon.
He remains in custody for questioning.
Anyone with information has been urged to call 101, quoting log number 0246 of June 30.
Alternatively, independent charity Crimestoppers can be contacted anonymously on 0800 555 111 or online at crimestoppers-uk.org.
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