NEW YORK (TheStreet) -- Some of the hottest private companies could go public before the end of the year, including fitness chain SoulCycle and mobile payments processor Square.

"Everyone is looking  at SoulCycle -- that's a growth company," said Kathleen Smith, principal of Greenwich, Conn.-based Renaissance Capital, which manages the Renaissance IPO ETF (IPO) - Get Report . 'We think SoulCycle is targeting for later this year and could have debuted after Labor Day, but I think decided to wait for some of the turbulence in the market to subside."

She said Square, the mobile payments company run by Twitter (TWTR) - Get Reportco-founder Jack Dorsey, is expected to debut as a public company later this year.

This week, Richmond, Va.-based food distributor Performance Food Group and Nashville-based surgical hospital operator Surgery Partners are set to go public, raising upwards of $350 million each.

Only three IPOs have priced in September, the lowest level since 2011, Smith said. While some big names are expected to go public towards the end of 2015, the market is still on rocky footing.

Activity is down 31% so far this year, compared to the same time last year, Renaissance said.  "IPO activity relates very closely to returns," she said. "Almost 60% of the 134 deals completed so far this year have broken their IPO price, leading to a lot of cranky IPO investors out there."

Some notable examples include e-commerce company Etsy (ETSY) - Get Report , which is down 53% since its debut back in April. Plus, chicken wing restaurant Wingstop (WING) - Get Report slumped almost 19% since its June IPO.

Smith's aforementioned exchange-traded fund has lost some 13% since the start of the year.

"The worries about what's happening with the Federal Reserve'slooming rate hike and a slowing global economy have weighed on the IPO market overall and on new issues," Smith added. "If we are seeing slightly slower growth, that is a worry to a leveraged company that may have very thin growth prospects."