March 27 (Bloomberg) -- Vonage Holdings Corp., the worst- performing U.S. IPO in the past year, may go bankrupt by 2009 and investors should sell shares of the Internet-phone company, said Citigroup Inc., a manager of the initial public offering.

Citigroup analyst Michael Rollins reduced his rating from ``hold'' in a note to investors yesterday and said ongoing patent litigation increases the risk to the Holmdel, New Jersey-based company's profitability. He also slashed his price target for the stock to $2.50 from $7 previously.