China's tennis darling Li Na on Friday blamed her recent up-and-down performance on her gender, saying female players were "not as harsh or as tough" as men as she signed a major sponsorship deal. Li, who became the first Asian to win a Grand Slam title when she triumphed at the French Open in June, made the comments at a news briefing announcing a two-year tie-up with Australian resort operator Crown. "Nowadays, female players are fluctuating in their performance remarkably," the 29-year-old told reporters in response to a question about her inability so far to replicate her winning ways in tournaments following the French Open. "That's attributable to the difference between the two genders," she said. "The female players are not as harsh or as tough as male players, they want to take some time to re-adjust themselves after a big victory in a big event." Li has not been able to add to her trophy cabinet following her French Open triumph, crashing out of major tournaments such as Wimbledon and the US Open. The Chinese tennis superstar -- who has a long line of local as well as international companies wooing her to front their products -- said she was "working on" winning tournaments to make her sponsors proud. "I'm glad to have attracted so many sponsors and I believe that the brands will choose the player that can best align with their image," she said. "The precondition is that I have to perform very well on the court so that they will be happy with me, and I'm working on that." Besides Crown, brands such as automobile firm Mercedes-Benz, luxury watchmaker Rolex and ice cream manufacturer Haagen-Dazs, as well as sports giant Nike have signed Li to be the face of their goods in China. Crown would not comment on how much the firm's deal with the tennis star was worth. Li?s agent had predicted in August that her endorsements over the next three years could top $40 million, perhaps eclipsing Russian superstar Maria Sharapova as the top endorsement earner in women's sports. But Li said she had not changed despite her fame and fortune. "I'm still the old Li Na, but nowadays people have higher expectations of me and are putting the label of a Grand Slam winner on me. I'm still a tennis player, it doesn't make a lot of difference," she said.