Officers were called to the station in Townmead Road on June 18 just after 5.20pm following reports of an assault.
At the scene a 20-year-old man was treated for stab injuries.
He was taken to hospital with serious injuries and has since been discharged.
British Transport Police officers believe the man in the CCTV image may have information which could help their investigation
Two men have previously been arrested and charged in connection with the attack.
Joseph Jakada, 21, of Cambridge Gardens, Kensington, appeared at Highbury and Islington Magistrates’ Court on July 4.
Aidan Watts, 20, of Cremorne Estate, Kensington, appeared at Inner London Magistrates’ Court on June 23.
Both were charged with Section 18 GBH and affray.
Watts was further charged with possession of a bladed article and Jakada was charged with possession of cannabis.
They are next due to appear at Inner London Crown Court on July 22.
Two other men were arrested on suspicion of attempted murder and later released on bail.
Anyone who recognises the man pictured or who has information that could help police, to get in touch by texting 61016 or by calling 0800 40 50 40, quoting reference 553 of June 18.
