Raducanu has two tournaments – the Pan Pacific Open in Tokyo and the Hong Kong Open – left on her schedule this year.
Francis Roig, who has an agreement to coach Raducanu until the end of the season, is not with her in Ningbo.
Raducanu has played 50 matches on the WTA Tour this year, the most since her breakthrough US Open triumph in 2021.
The physical demands may be starting to show, with Raducanu’s movement falling away as former top-40 player Zhu extended the rallies to keep her on court for longer.
Raducanu won only 51% of points on her first serve and 38% on her second.
She raced into a 3-0 lead and served out the opening set despite four breaks of serve in the final five games.
She and Zhu exchanged breaks early in the second set before Raducanu asked for the physio. She left the court after Zhu forced a decider.
Raducanu grabbed at her back early in the third set after running for a forehand, and she made more errors as the match went on.
Zhu faces Russian top seed Mirra Andreeva in the last 16 on Wednesday.
