Gap Inc chief executive Art Peck is to exit the fashion group amid tumbling sales and ahead of an expected spin-off of Old Navy.

Peck is to leave Gap after “a brief transition” and Robert J Fisher, a member of the retailer’s founding family and chairman of the business, will take over on an interim basis.

The switch came as Gap reported a fall in third-quarter like-for-like sales, the latest poor performance over a longer-term period.

Peck has been with Gap for almost 15 years and became chief executive in 2015, but the retailer’s valuation has plunged during his time in charge.

Fisher maintained: “Under Art’s tenure, we have made progress investing in capabilities that bode well for the future such as expanding the omnichannel customer experience and building our digital capabilities.”

“As the board evaluates potential successors, our focus will be on strong leadership candidates with operational excellence to drive greater efficiency, speed and profitability.

“In the meantime, we will continue to focus on leveraging the power of our brands and the talented teams that lead them to improve execution and better position the portfolio for growth.”

Gap said Fisher “brings strong leadership and invaluable perspective from his 35-year history with Gap Inc”.

He has held positions including interim president and chief executive, and has been on the board since 1990.

Gap reported comparable sales down 7% at the eponymous business, down 3% at Banana Republic and down 4% at Old Navy.

Gap Inc chief financial officer Teri List-Stoll said: “This was a challenging quarter, as macro impacts and slower traffic further pressured results that have been hampered by product and operating challenges across key brands.

“We have tremendous confidence in our brands and the talented organisation that supports them, and we are seeing progress in some key areas. However, there is more work to do to leverage the capabilities we have invested in and deliver the profitable growth we know these brands are capable of delivering.”