Shanghai-based Fosun International Ltd said Thursday it had assured its stake in Focus Media by signing a rollover agreement Wednesday, in response to Focus Media's Wednesday announcement of a $3.7 billion privatization which will be the largest leveraged buyout in China.

The US-listed Focus Media, a leading Chinese display-advertising provider, posted on the NASDAQ Wednesday that it had approved an acquisition by Giovanna Parent Ltd with an offering price of $27.50 per American depositary share. Each ADS represents five ordinary shares. The privatized shares will be bought by a consortium of six major parties including Fosun and Focus media's CEO Jiang Nanchun.

Fosun, currently the second largest shareholder in Focus, immediately signaled support for the transaction by pledging Thursday to "subscribe for 174,084 new shares of Giovanna Group Holdings Ltd, delivery of which shall constitute full consideration" for its current 17.2 percent stake in Focus Media. Fosun signed the agreement to roll over the shares with Giovanna Group and its subsidiary Giovanna Parent.

This transaction will enable Focus to become a privately held company and delist from the NASDAQ, which the company expects will occur in the second quarter of 2013.

Approximately 36 percent of Focus shares are held by Fosun, Jiang, and some of Focus' senior managers, so the acquisition and privatization is likely to be approved, said Focus Wednesday.

But Hao Junbo, an experienced US securities litigation lawyer, said it is still hard to tell whether the transaction will be approved, given that some Focus shareholders may not accept the offer, which he believes is not high enough for such a big company.

Soon after Focus got its first offer of $27 per ADS on August 31, Hao and his US peers began working together to provide legal services for shareholders who were disappointed with the offer.

"Early in October, one Focus shareholder in New York, who held 37,000 shares according to the offering price on August 31, asked about such services via e-mail," said Hao.

Approval of the deal requires an affirmative vote from shareholders representing at least two-thirds of Focus' shares.

The offer of $27.50 per ADS could satisfy the interests of Focus' shareholders, who should be in favor of the approval, Zhong Rixin, an analyst at Beijing-based consultancy imeigu.com, told the Global Times.