Zverev was trailing 7-6(8) 6-6 against Nadal when he rolled his ankle and he screamed out in agony.
The world No.3-ranked player posted an image on Instagram of him alighting from a private plane walking on crutches.
Zverev cried in pain following the fall and had to be assisted into a wheelchair by the physio and Nadal, who quickly made his way round the net to help support the 25-year-old.
Zverev had to be pushed off the Philippe Chatrier court on a wheelchair after twisting his ankle late in the second set as he trailed 7-6(8), 6-6 in his meeting with 21-time Grand Slam champion Nadal.
Nadal was leading 7-6(8) 6-6 when Zverev suffered the injury.
The German defeated his Spanish opponent, 6-4 6-4 4-6 7-6(7).
The 19-year-old is the youngest player since start of the ATP Tour in 1990 to defeat three top-five players at the same event.
Zverev kicked out of the ATP 500 event in Acapulco after he smashed his racket repeatedly against the umpire's chair after a doubles defeat.
Nadal has reached his 14th quarterfinals of the Australian Open.
Osaka will next face Amanda Anisimova, a 20-year-old American who beat Olympic gold medalist Belinda Bencic 6-2, 7-5.