Officers had released an appeal with a CCTV image of a person they wanted to speak with in connection to the incident, which happened on the 295 bus on December 20 in Fulham Palace Road.
Following the Metropolitan Police appeal, an 18-year-old man attended Harrow police station on Friday May 19.
Police confirmed he had not been arrested and will be interviewed under caution in due course.
Officers say they are satisfied the man is the same as the person shown in the CCTV image.
The attack happened at 4.40pm, and left the victim with cuts and bruising to her lips.
She was taken to a west London hospital by ambulance for treatment.
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