Two-time Grand Slam champion Elena Rybakina retired injured from her Cincinnati Open quarter-final against Iga Swiatek on Thursday, ending her chance of taking over as world number one.
Rybakina retired with an ankle problem while trailing Swiatek 4-1.
She needed to reach the final to overtake Aryna Sabalenka at the top of the rankings. The Belarusian had already been knocked out in the last 16 at the tournament in the US state of Ohio.
Rybakina said the injury had been troubling her for some time but she had felt it was under control before the match. The 27-year-old said walking was painful and that she would undergo an MRI scan.
Rybakina won Wimbledon in 2022 and the Australian Open earlier this year.
The US Open, the final Grand Slam tournament of the season, begins in New York on August 30.