Cirstea, who is currently ranked 38th in women's singles, made the comments on Romanian podcast "La Fileu" last week while discussing advertising contracts handed out to tennis players.
Reuters has contacted Adidas for comment.
The Romanian, formerly sponsored by Adidas, said American, Chinese, Japanese and British players are the best-paid, but "Eastern Europe doesn't really sell".
"I remember, for example, when I had a contract with Adidas, considering that I look fairly good for an athlete, they were telling me that it's better to look good and be in the Top-20 than to not look that good and be number one," Cirstea said.
"When you are in the Top 20 you are seen anyway, you are there at every tournament, and they were telling me it's better to be beautiful in Top 10, Top 20 than less beautiful and number one.
"Of course, you realise they have their own quotas, it's a market."
Cirstea reached a career-high ranking of 21 in 2013.
