19-year-old world No. 33 Madison Keys was forced to pull out of her second-round match at the Apia International in Sydney after injuring her shoulder.

Bad luck for @Madison_Keys, forced to retire against @TPironkova with a right shoulder injury. Get well soon Madison! #SydneyTennis

— Apia Intl Sydney (@SydneyTennis) January 13, 2015

This from Madison Keys: "Just hit a serve weird and just kind of impinged my shoulder a little bit." #SydneyTennis

— Apia Intl Sydney (@SydneyTennis) January 13, 2015

Thanks for all the messages guys! Going to rest up to be ready for @AustralianOpen! 🎾

— Madison Keys (@Madison_Keys) January 13, 2015