Margo Georgiadis has left her job as Groupon’s chief operating officer to return to Google, her previous employer, the daily deal provider says.  She had started at Groupon five months ago, in April.

She returns to Google as president of the Americas, Groupon says. Before coming to Groupon, she was the search engine’s vice president of global sales operations, a job she’d held since 2009. Groupon gave no reason for her departure, and neither Google nor Georgiadis provided immediate comment.

“Groupon is a great company and I feel privileged to have worked there even for a short time,” Georgiadis wrote in a message posted on the blog of Groupon CEO Andrew Mason. “It was a hard decision to leave as the company is on a terrific path. I have complete confidence in the team’s ability to realize its mission.”

Mason writes that Groupon so far this year had hired eight executives, including Georgiadis. “We’ve built a fantastic team that has proven itself highly capable, so this change won’t have an impact on operations,” he writes. “In fact, we are using it as an opportunity to reorganize in a way that reflects our evolving strategic priorities. Sales, channels, international and marketing will now report directly to me.”

Groupon, on Friday, restated its revenue for the first half of 2011, to $688.0 million from $1.5 billion. In a financial filing, the daily deal provider says it reduced its revenue figure because its accounting now includes subtracting the merchant’s cut from Groupon discounts. For 2010, Groupon reduced its reported revenue to $312.9 million from $713.4 million. The company is in a quiet period ahead of its initial public offering. Groupon typically retains half of what a consumer pays for a voucher and the merchant or service provider offering the voucher gets the other half.