After seeing the 34-year-old, the woman is believed to have texted a friend, who instantly sent a message to the centre-back on Twitter.
Eurosport journalist Tom Adams has claimed that Ferdinand then approached the girl on the carriage to introduce himself and discover more about her charity.
When asked on the social network site if the story was true, Ferdinand replied: "Yep, news travels fast on this Twitter! See if I can help out."
Ferdinand is believed to have suggested that he could help with the promotion of the charity.