Tunisian tennis star Ons Jabeur retired hurt during the Sydney Classic semi-finals on Thursday, days before the Australian Open. Jabeur was playing the in-form world number seven Anett Kontaveit, who won a tight first set 6-4 before the Tunisian called for a medical timeout. After lengthy treatment on her lower back, Jabeur forfeited the match. It is a big setback for Jabeur, with the opening Grand Slam of the year starting on Monday. She had a breakthrough 2021, when she won her maiden WTA singles title and surged into the top 10 for the first time. Kontaveit will now play world number four a…