Play was suspended on all outdoor courts on Monday because of the heat.
Raducanu posted a screenshot of her phone that showed a temperature of 34C.
Defending champion Jannik Sinner retired with cramp in the third round of the Shanghai Masters this week, while 24-time Grand Slam champion Novak Djokovic vomited during his win over Yannick Hanfmann.
A deep run in Wuhan would have boosted Raducanu’s chances of being seeded for January’s Australian Open, the first Grand Slam of the season.
The 2021 US Open champion broke in the first game before Li won six successive games – dropping only one point on serve – to wrap up the opening set in 28 minutes.
Raducanu looked fatigued as she recovered from three double faults to hold serve at the start of the second set.
But she failed to convert two break points in the next game and a series of sluggish unforced errors then helped Li break for a 2-1 lead.
A double fault handed Li another break, and Raducanu called for a medical timeout before retiring.
“I hope she feels better. I don’t know what happened, but you could tell towards the end she was maybe not moving as much,” world number 46 Li said.
She will play Russian ninth seed Ekaterina Alexandrova, who beat Canadian teenager Victoria Mboko 6-3 6-2 on Monday, in the second round.
Earlier on Tuesday, Japanese four-time major winner Naomi Osaka beat Canada’s Leylah Fernandez 4-6 7-5 6-3 to reach round two.
Polish second seed Iga Swiatek beat Marie Bouzkova of the Czech Republic 6-1 6-1, while American 14th seed Emma Navarro suffered a shock 6-2 2-6 6-3 defeat by world number 142 Shuai Zhang of China.
