Kara Swisher of All Things Digital is reporting that Yahoo! may be on the verge of acquiring Citizen Sports.

Specifically, she says that “according to numerous sources inside and outside the company,” Yahoo! is ready to buy “an online sports site this week.”

Per Swisher, Yahoo! and Citizen refused comment, but the report seems fairly strong and comes from a reporter with a Wall Street Journal background.

Citizen Sports, of course, first came to market as ProTrade back in 2004, led by a stock market-style sports game. Since then, Citizen has set its sites on social media. In November 2008, the company bought a trio of competitors and has since focused on Facebook and smart-phone applications, and ended ProTrade.

Swisher reports estimates of Citizen’s value from $40 million to $50 million. She also reports that Yahoo! CEO Carol Bartz is the keynote speaker at this week’s IMG World Sports Congress, which means we should find out for sure soon.

FSB.com will share more as we become aware.