Simona Halep shocked the tennis world by announcing her sudden retirement following a first-round defeat at the WTA Cluj-Napoca tournament.

Taking the microphone after her loss, the two-time Grand Slam champion delivered the unexpected news to a tearful home crowd in Romania.

โ€œTonight, I don't know if it's with joy or sadness, I think both feelings are trying me but I'm making this decision with my soul,โ€ Halep announced.

โ€œWhere I probably was, it's very hard to get there and I know what it means to get there. That's why I wanted to come here today in Cluj to play in front of you and say goodbye.โ€

Despite a tough 6-1, 6-1 loss to 72nd-ranked Italian Lucia Bronzetti, Halep remained grateful as she addressed the crowd.

โ€œI don't want to cry. It's a beautiful thing. I became world number one, I won grand slams, it's all I wanted. Life goes on, there is life after tennis and I hope that we will see each other again.โ€

The 33-year-old's career hasn't been without controversy, facing separate bans after testing positive for roxadustat at the 2022 US Open - later reduced to nine months on appeal - and for โ€œirregularitiesโ€ in her biological passport data.

Halep retires with 24 singles titles and more than $AUD63 million in prize money.