Shares of Walmart are slipping in Tuesday trading after the retailer announced that chief merchandising officer Duncan Mac Naughton is stepping down, just days before the kickoff to the holiday shopping season on Black Friday. Walmart said Mac Naughton, who joined the company in 2009, is leaving to pursue new opportunities. Walmart U.S. chief executive Greg Foran said he has decided not to name a new chief merchant at this time. Instead, Foran said he will relook at the company's merchandising structure and take this opportunity to get closer to the merchandising team. Effective immediately, Foran said all leaders in the division will report directly to him. He also announced that EVP of General Merchandise Steve Bratspies will take the EVP of Food role from Jack Sinclair, who will take another role at the company.