FILE PHOTO: Greg Foran, president and CEO of Walmart U.S., speaks about the company's Black Friday plans at a Walmart store in Secaucus, New Jersey, November 11, 2015. REUTERS/Lucas Jackson

WASHINGTON (Reuters) - Walmart Inc WMT.N said on Thursday its chief executive for U.S. operations, Greg Foran, will leave the company early next year and be replaced by the head of its Sam's Club warehouse chain unit, John Furner.

Foran’s departure is likely to be considered a blow for Walmart given the New Zealand native is credited with turning around Walmart’s U.S. business by focusing on improving existing stores. Walmart reported 20 quarters of comparable sales growth under his leadership.

Foran, who has held the job since 2014, will stay with Walmart until Jan. 31 and then take on the role of chief executive at Air New Zealand Ltd (AIR.NZ), an appointment that was also announced separately by the airline.

Walmart Inc Chief Executive Doug McMillon said Foran’s ability to innovate, including using new technology, “has helped position us for the future.”

However, some investors were skeptical of the change in leadership.

"While we've been highly impressed with Mr. Furner's work at Sam's Club... he does admittedly have big shoes to fill," said a note from Jefferies Group LLC JEF.N. "We can't help but expect the market to react negatively to today's news."

Furner has run the $57.8 billion Sam’s Club business since 2017. Over that time, he has improved the unit’s performance with higher comparable sales by pushing the retailer to innovate, shutting stores, and repurposing stores as distribution hubs.

Walmart in August raised its forecasts for U.S. comparable sales for the full year. Its shares have risen 28% so far this year.