Top seed Angelique Kerber will lose her world number one ranking after being beaten by Spain's Garbine Muguruza in the fourth round at Wimbledon.
Muguruza, the 14th seed and a runner-up at SW19 in 2015, won an enthralling match 4-6 6-4 6-4 in two hours and 20 minutes on court two.
The German, a finalist in 2016, had needed to reach Saturday's final to have a chance of retaining her ranking.
Muguruza, 23, will play Svetlana Kuznetsova of Russia in the last eight.
If Halep does not reach the last four, 25-year-old Karolina Pliskova of the Czech Republic will move to top spot despite her second round exit at Wimbledon.
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