The American world number one withdrew during her first-round match at the Wuhan Open due to a viral illness.
Williams' fitness will be closely watched at the WTA Premier tournament played on hard courts in Beijing. The 18-time grand slam champion would be a deserved favourite to win the title for a third time if she was healthy.
Li Na's retirement means the event is missing the high-profile local and two-time grand slam champion.
The other nine players in the world's top 10 - Williams, Simona Halep, Petra Kvitova, Agnieszka Radwanska, Maria Sharapova, Angelique Kerber, Eugenie Bouchard, Ana Ivanovic and Jelena Jankovic - are in the field though.
Canada's Bouchard and Czech Republic's Kvitova have enjoyed good runs in Wuhan in the lead-up.
Jankovic, the Serbian world number 10, is the 2008 champion and two-time runner-up – including last year. Williams beat Jankovic 6-2 6-2 in the 2013 showpiece.
Poland's Radwanska is another player with a good record at the tournament, which she won in 2011 and was runner-up at two years earlier.
Hard-hitting Ukrainian Elina Svitolina, who has been good in Wuhan, is a player to look out for.
Williams will be hard to beat if she is fit, though, and all eyes will be on her as she looks to defend her title.