The singer is said to be "royally p**sed off" after Brown released a statement following allegations that he assaulted her.
Despite saying that he was "sorry and saddened" by his actions, sources close to Rihanna have insisted that he has not gone far enough.
"'All of us, including Rihanna, don't understand how he can say he's sorry on the one hand, but still ... does not admit any guilt," Metro quotes a friend as saying.
"He should have expressed more contrition."
Brown is expected to appear in court on March 5.