The model arrived at the Pink Elephant venue during a night out, but bouncers for the club decided it would not be a good idea to have the two women in the hotspot at the same time, according to the New York Post.
Tran's representative reportedly told eyewitnesses, "She was told she could (not) attend said club, because Rihanna was inside. (She) decided to go elsewhere."
A spokesperson for the club confirms, "She wasn't let in as a courtesy to Rihanna. To keep the peace, they decided it was in everybody's best interest if they weren't on the dance floor at the same time."
Singer Brown began dating Tran in 2011, two years after his highly-publicised split from Rihanna in 2009.
He reconciled with the Umbrella beauty last year (12), prompting Brown to dump Tran, but the reunion didn't last long and he subsequently revived his relationship with the model earlier this year (13).