CHICAGO (Reuters)—Groupon Inc., which runs the world's largest online coupon website, was sued on Tuesday by a shareholder who accused the company of misleading investors about its financial prospects and concealing weak internal controls.

Just four days ago, Groupon unexpectedly revised its results for the fourth quarter, its first as a public company to a bigger net loss and said it had a "material weakness" in its internal controls, having failed to set aside enough money for customer refunds.

According to a complaint filed in federal court in Groupon's hometown of Chicago, the company overstated revenue, issued materially false and misleading financial results, and concealed how its business was not growing as fast and was not nearly as resistant to competition as it had suggested.

Julie Mossler, a Groupon spokeswoman, declined to comment. The company has said it does not discuss pending litigation. Several other law firms have said they may file similar lawsuits.

Groupon in November pulled off one of the largest Internet IPOs of the past decade, valuing the company at the time at well over $10 billion.

However, the leader in the fast-growing Internet daily deals space populated by rivals such as Amazon.com Inc and LivingSocial was criticized by some analysts and investors for aggressive accounting in the run-up to the IPO.

The complaint said Groupon did not reveal its "poor and inadequate" internal controls, and concealed in its registration statement and prospectus for its November 2011 initial public offering that it did not comply with various countries' laws.

The lawsuit seeks class-action status on behalf of shareholders who acquired Groupon shares between Nov. 4, 2011, and March 30, 2012.

Shares of Groupon, which lost 16.9% on Monday after the company announced late Friday its results revision, fell 1.7% on Tuesday to close at $15.02. The stock is now roughly 25% below the $20 IPO price.

Among the other defendants are Groupon Chief Executive Andrew Mason and several banks that helped take the company public, including lead IPO underwriters Credit Suisse, Goldman Sachs and Morgan Stanley.

The plaintiff is Fan Zhang, who said he paid nearly $61,800 for 3,000 Groupon shares in February, and sold them in March at a loss of more than $9,000.

On March 29, Groupon agreed to an $8.5 million settlement of nationwide litigation alleging the expiration dates on its coupons are illegal.