It happened when the 24-year-old was leaving a night club here with her model friend Cara Delevingne Saturday night.
Rihanna's bodyguard's leg was also said to have been injured as he attempted to catch her attacker. The crazy fan allegedly shouted something about Rihanna's boyfriend Chris Brown before throwing the bottle at her.
Brown, 23, is still on supervised probation for physically assaulting her in 2009.
"The bottle caused Rihanna to stumble into a metal crate and slice open her leg. Rihanna's bodyguard immediately went after the crazed fan, but hurt his leg going after the subject. Rih's guard was taken to a London hospital for treatment, and the mad man is still on the loose," reports contactmusic.com.
Rihanna was here to launch her fashion line for River Island at London Fashion Week.