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World No 5 lost her second group league encounter 18-21, 19-21 to World No 61 Ukraine's Maria Ulitina to crash out of the competition.
"I had a knee pain and could not give my best. It was heavily strapped, and I tried my best. My movements were not smooth and were painful. It's heartbreaking loss. I also feel very bad about it," Saina said.
The injury according to her happened during training before the Olympics and it got worse during the match.
"It happened just before the Olympics about one and half weeks back. It happened during training and got aggravated after coming here," she said.
Saina agreed that she was not able to move well but credited her opponent for playing well.
"She played better but I was not able to move on the court. I tried for improvement but was not successful."