Wal-Mart, the world’s largest retailer, faces “really big challenges” if it is to maintain its success, former chief financial officer Jack Shewmaker has warned.

Shewmaker, who is still a Wal-Mart director, pinpointed a raft of concerns that he urged the store group to address. “The world is changing. Wal-Mart has to change, but I’m not sure it’s changing fast enough,” he said.

Top of the list, Shewmaker told the World Retail Congress in Barcelona, “is doing what Sam Walton never did – underestimating the competition”.

He cautioned: “When we get in that position, we undervalue new concepts from a new field of competitors. You need to do what Sam did and look at what [competitors] do better than you. Before you say ‘that won’t work for us’, think about it.”

Shewmaker also voiced concern about Wal-Mart’s and other retailers’ “failure to succinctly meet customers’ needs in core markets” and the threat posed by failing to reinvest in their core business, because of “getting caught up in growth mode”.

He said retailers should constantly invest in their operations, even during downturns. “The luxury of not doing anything to a store for 15 years doesn’t exist anymore – it’s down to less than five,” Shewmaker argued. “You need to take your capex budget apart and make sure you’re rejuvenating your core business”.

He flagged the need to communicate effectively with all stakeholders, ranging from suppliers to customers, staff and investors.

“Don’t get overly focused on one segment so you slight another. Wal-Mart has been guilty of that over the years,” Shewmaker said.

He believes the biggest issue facing retailers is the breakneck pace of change and that those that fail to adapt quickly would be consigned to the dustbin of history.

“If you’ve got the same model you had five years ago, I’d take another look,” he advised. “The customer is changing. You’ve got to put your vote in the merchandise categories that are important to today’s consumer.”