The British Transport Police previously released an image of the pair, a man and woman, and launched an appeal to identify them following an incident on October 11.
Officers wanted to question them about an assault on a woman who was with her sister and two young children, one of whom was in a pushchair, at the entrance of Bond Street Tube station.
BTP have now said they believe the pair left the country after the assault.
It is believed the man left the UK on October 14 and the woman on October 24, a spokesperson for the force said.
This was before BTP published their media appeal.
Officers said they believe the man and woman “do not reside in the UK”.
The incident started when a man and woman were walking together in front of the family into the station and the woman collided with the pushchair at around 7.30pm.
The man then began shouting racial abuse at the victim and her family, before the woman grabbed her hair, police said.
When the victim tried to defend herself the man pulled out a small bottle and said it was pepper spray before spraying it in the direction of the victim and her family, officers said.
BTP said the woman shouted abuse and made lewd gestures at them before both groups left the scene.
A spokesperson for the force said: “We continue efforts to make contact with and speak to them, and from there we will determine the next steps in the investigation.
“We are in contact with the victim and her family and are keeping them updated regularly as the investigation continues.”
