Practice isn't confined to the court when Novak Djokovic and Alexander Zverev get together.
The world No. 1 took time out from training on Arthur Ashe Stadium court to test Zverev's hands.
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Watch the 17-time Grand Slam champion launch a few balls up into the stands where Zverev was waiting.
The pair are both scheduled to play the Western & Southern Open, which starts on Thursday, and the US Open beginning on August 31st.
The Western & Southern Open moved from Cincinnati to the Billie Jean King National Tennis Center in New York due to Coronavirus safety protocol.
Photo credit: Adria Tour Facebook