Goldman Sachs Group Inc. and Morgan Stanley may lead a second-half initial public offering (IPO) that could value Groupon Inc. at $15 billion to $20 billion, Reuters reported.

Citing an unidentified source, Reuters said the daily deals website could raise as much as $1 billion in the IPO, which is expected to come in the second half of 2011.

The exact size has yet to be determined, said the source, who warned that the size of the IPO and the market value of the company were not final and were subject to change.

According to The Wall Street Journal, JPMorgan Chase & Co was also expected to have a co-manager role.

The latest valuation of Groupon comes amid rising valuations of other popular Internet companies such as Facebook and Twitter, and concerns that the companies won’t be able to justify their sky-high assessments.

Groupon, which in December rejected a $6 billion buyout offer from Google Inc., has been profitable since June 2009, Reuters said.