The We Found Love singer apparently wept as she recalled the 2009 attack which resulted in Chris being sentenced to five years' probation and community service.
In the US TV interview, to air this Sunday, Rihanna reportedly revealed she felt "angry, hurt and betrayed" after the R&B star assaulted her before the Grammy Awards in LA.
"It was embarrassing, it was humiliating. I lost my best friend," The Sun quotes Rihanna as saying.
"As angry as I was, I just felt like he made that mistake because he needed help. And who's going to help him?
"Everybody's going to say he's a monster, without looking at the source. And I was more concerned about him."
Earlier this year, Rihanna caused controversy when she collaborated with Chris. She was also rumoured to have had a rendezvous with the singer on a yacht in the South of France last month.