Osaka made global news last month when she beat the legendary Serena Williams in Flushing, N.Y.in a match that drew controversy.
The Japanese star required treatment to her lower back during her semi-final defeat to unseeded Anastasija Sevastova at the China Open in Beijing on Saturday.
It is a place that she is not altogether comfortable in.
Afterwards, Osaka, who turns 21 on October 16, said it was more a case of fatigue than anything more serious, but suggested that she may not make the WTA Hong Kong Open, which starts on Monday.
"If you don't win a tournament, then people will say, "Oh, she hasn't won a tournament".
On Friday, Osaka was unhappy with her performance in Friday's quarter-final win over Zhang Shuai.
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"Then if you win one Grand Slam, they're like, 'Oh, she only won one Grand Slam'".
Osaka added, "I know it's bad but I sort of read the comments. I'm just, like, "Oh, I guess I have to do more, to be better".
Osaka, who was attempting to reach a third straight final after NY and Tokyo's Pan Pacific Open, was unhappy with her behaviour in Friday's quarter-final victory over Zhang Shuai. She was close to tears during the second set and tossed her racquet, AFP reported.
"But my back's sort of been bothering me since the beginning of the tournament".
Top seed Juan Martin del Potro will be the strong favourite when he faces unseeded Georgian Nikoloz Basilashvili in the men's final later on Sunday.
Fognini, who was chasing a fourth title of the season, reportedly has an ankle injury.