Draper reached his first Grand Slam semi-final at the US Open this month, when he lost in straight sets to world number one Jannik Sinner.
After vomiting on court three times during the match, he said he would “really look into” his sickness issues, although it is not known whether the problem in Tokyo is related.
Draper was also sick immediately after his Australian Open first-round victory in January, which he said was because of “psychological stress”.
World number three Carlos Alcaraz will face Russia’s Karen Khachanov in the quarter-finals of the China Open.
Spaniard Alcaraz beat Dutchman Tallon Griekspoor 6-1 6-2 in the last 16 in Beijing.