Sam Stosur is set to lose her place as Australian No.1 following a French Open fourth round defeat at the hands of teenager Jelena Ostapenko.

Stosur, who reached the semi-finals at Roland Garros last year, cruised to the opening set but then collapsed to crash out 2-6 6-2 6-4 against her young Latvian opponent.

The Queenslander was struggling with a hand injury, but was blasted off court as 46 Ostapenko winners flew past her.

To add to Stosur’s dismay, she is now likely to drop below compatriot Daria Gavrilova when the official rankings are released after the French Open is completed.

Stosur was defending a massive 770 points from last year’s deep run in Paris, and started the 2017 tournament just 190 points ahead of Gavrilova.

Gavrilova lost in the first round against Belgium’s Elise Mertens but had no points to defend at Roland Garros and should now be the top ranked Australian when the new list is announced next week.

Stosur has been the Australian No.1 for 450 weeks and recently defeated Gavrilova in the final of the Strasbourg International.