An Australian tennis player allegedly threatened to post nude photos online of his former US girlfriend.

An Australian tennis player has been charged in the US with aggravated stalking after allegedly threatening to post nude photos of his ex-girlfriend online.

Mark Terry Henderson, 32, was Australia’s top-ranked junior in 1999 and went on to play at the University of Tennessee and Illinois’ DePaul University before becoming a coach at Northwestern and Western Michigan universities.

The Chicago-Tribune reports that Henderson had been in an on-again, off-again relationship with the 29-year-old Chicago woman for more than five years before she broke up with him in February.

Henderson has been living in Brisbane, but allegedly harassed the woman with phone calls, emails, and texts, including threats to her life, prosecutors alleged.

At one point, he sent the woman a collage of naked photos of her and threatened to post it online if she did not send him more nude images, prosecutors said.

Police in Chicago and Australia contacted him, but he allegedly continued the harassment.

On May 6, Henderson flew to Chicago and the next day police found him sitting outside the woman’s parents’ house, it is alleged.

Prosecutors said later that day Henderson approached the woman, threatened her life and grabbed her before she ran to her car and locked the doors.

Henderson then went around and tried all of the car’s door handles, prosecutors said, but the woman was able to escape and call police.

A warrant was issued, Henderson was arrested in Tennessee and extradited back to Chicago on Thursday where a judge granted him $US500,000 ($A540,980) bail if he surrendered his passport, refrained from using social media and undergo GPS monitoring.

Henderson, who starred at Essendon Keilor College in Melbourne, was the number one ranked junior player in Australia in 1999, according to his University of Tennessee biography.