The ride-hailing service confirmed Monday that its CFO is stepping down. Callinicos, who joined Uber from Google (GOOG) in 2013 and also previously worked at Microsoft (MSFT), helped the company expand its global operations to more than 50 countries.

In an e-mail sent to investors Monday by Uber CEO Travis Kalanick said that the company has not named a replacement CFO, but that Gautam Gupta, Callinicos’ “right hand on Strategic Finance,” will be Uber’s acting head of finance. (Gupta is a former Goldman Sachs VP who also joined Uber in 2013.) In the e-mail, which was reviewed by Fortune, Kalanick said Callinicos will stay on in an advisory role with Uber. In an e-mail to the company, Callinicos said he is leaving to spend more time with his wife and daughter.

Under Callinicos’ financial direction, Uber has raised more than $5 billion in funding and seen its valuation grow to $41.2 billion as it leads the current wave of tech industry “unicorns” — aka, startups worth more than $1 billion.

Given Uber’s massive valuation and recent growth, the company is at the top of the list of companies investors are hoping to see go public sometime in the near future. And, it did not take long for the industry’s surprise over Callinicos’ abrupt departure to give way to speculation over whether or not he is stepping aside to make room for a CFO with more Wall Street experience who can take the company public. While many investors have eagerly awaited a potential Uber IPO, The Street noted that a CFO switch could actually delay such a move.

In his e-mail to the company, Callinicos said he would “step back” and “let someone else take this amazing company to the next level as CFO.”