The 27-year-old singer was punched in the face by a man pretending to be a fan in 2009 as she autographed copies of her autobiography Dreams at a London book shop.
Although she only received minor bruising in the attack, Lewis admitted that the incident has had a long-term effect on her psychologically.
She told The Sun: "I'm definitely more aware when I go out in public and it has 100% had an effect on me and my life.
"But I've just got to deal with it. I don't like going out where it's really, really crowded. I'm obviously very suspicious of any men who look a bit dodgy."
Lewis was speaking as she signed copies of her new album Glassheart at HMV on London's Oxford Street on Monday, in what was her first public signing since the 2009 incident.
"I don't feel like anything is going to happen to me but being in that situation brings back memories," she noted.
Watch Leona Lewis discuss Glassheart with Digital Spy below: