The Japanese star had received treatment during a medical timeout in her third-round win over Elise Mertens and said the problem troubled her more in her 6-1, 6-4 loss to Rybakina.
"The last match I played, I felt a lot in my leg," Osaka said. "Then this morning, it just got a lot worse. I felt like I played the best that I could given the situation.
"I can't really push off like I want, and when I land, it hurts a little," Osaka added. "I was trying to figure out ways to, I guess, minimize it. I thought if I served a little slower the impact when I land would be less."
Reigning Australian Open champion Rybakina needed just 66 minutes to get past Osaka, who is hopeful she can manage the injury through the end of the season.
"Yesterday I got an ultrasound, and then I got an ultrasound again just now, and I'm probably going to go get an MRI, because, honestly, I don't really know too much about what's going on," she said.
"Thankfully we're at the end of the year, so after the Asian swing, we do get two weeks off. I'm just going to make do with the time that I have and try to be smart about the amount of matches I play."
More than two years since she returned to the tour after an extended maternity leave, Osaka said she is pleased with her Grand Slam season.
She exited the Australian Open in the third round but made the last 16 at Roland Garros and had a best-ever quarter-final run at Wimbledon that included a vitory over top-ranked Aryna Sabalenka.
"I started the year injured," she said. "I don't know if this counts as ending the year injured, but I definitely learned a lot about myself, about my tennis.
"I got the furthest that I've ever gotten in the French and in Wimbledon. Hopefully I can continue to build on that and just play more matches with these really good players, because I feel like I need those under my belt."
