Super sleuths on the internet reported it was 25-year-old Twilight star Kristen Stewart.
A report on Jezebel sketchily suggested Neeson and Stewart visited New York nightclub Tao NYC at the same time on January 5.
But a representative for Neeson told GossipCop the rumour was "stupid".
The same rep told The Independent it was the result of "meaningless speculation".
Despite the denial, Twitter quickly lit up over the rumours.
Neeson started dating Richardson, of the famous Redgrave acting dynasty, in the 1990s, with the pair marrying in 1994.
The couple had two sons together, Michael and Daniel. However, Richardson died in 2009 from brain injuries after falling on the ski slopes in Canada and bumping her head.
Stewart's previous relationships include her Twilight co-star Robert Pattinson and a brief liaison with Snow White and the Huntsman director Rupert Sanders.
She has reportedly split up with her girlfriend Alicia Cargile.
- News.com.au