Zayn, 22, allegedly sent Chloe, 23, flirty messages shortly after his split from fiancé Perrie Edwards earlier this month.
Now fans of the former One Direction star are said to have been targeting Chloe – leaving her shaken.
A source told The Sun: “Chloe has been really upset by the threats, particularly as she did nothing wrong.”
Zayn left Little Mix singer Perrie, also 22, heartbroken when he ended their three-year engagement by text, and was allegedly quick to move on.
He apparently messaged former Celebrity Big Brother contestant Chloe: “Do you have a boyfriend at the mo?”
Chloe, who is in a relationship with Scunthorpe United footballer Jordan Clark, was quick to dismiss Zayn’s messages.
An insider said: “Chloe was shocked by the messages. She knew Zayn had only just split from Perrie and couldn’t believe he was already looking elsewhere.
“She told him she had been with her boyfriend for a long time. He seemed to accept that, and told her if he hadn’t asked he would have ended up being ‘rude’.”
Earlier this week Perrie – who has been in America on promotion – broke down during a performance with the band, proving that the split has finally become too much for her.