Girls Aloud singer Nicola Roberts said she didn't lie to protect Cheryl Tweedy at the star's trial on Thursday.
Cheryl is accused of racially abusing and hitting toilet attendant Sophie Amogbokpa. Nicola, 18, claims she was fighting back after being hit twice.
On Wednesday Tweedy said she had only been hit once during the incident in a Surrey nightclub in January.
When prosecution lawyers accused her of not telling the truth, Roberts said "I'm not going to lie for anybody".