Western & Southern Open News
Tsitsipas leads the Zverev 6-2 in their ATP head-to-head rivalry.
Osaka's decision follows protests over the police shooting of Jacob Blake, a Black man, in the city of Kenosha, Wisconsin, on Sunday.
The Japanese tennis star defeated Anett Kontaveit 4-6, 6-2,7-5 on Wednesday to reach the semi-finals.
Two-time Grand Slam champion Osaka was due to face Elise Mertens in the last-four of the Western and Southern Open.
2020 Western & Southern Open is scheduled from August 20-28, 2020.
Main draw play for the tournament will begin on August 22.
It was the Russian tennis star's second ATP Masters 1000 final appearance in as many weeks and third straight tour-level final appearance following the Citi Open and the Rogers Cup.
Osaka, who made back-to-back quarter-final finish in Toronto and Cincinnati, will now shift her focus on the US Open, which is slated to take place from August 26 in New York.
Djokovic will now lock horns with Frenchman Lucas Pouille for a place in the semi-final of Cincinnati Open.
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