"They've got the biggest online business in the country outside of Amazon. And they're growing it faster than Amazon is growing their online business," said Jan Kniffen, chief executive of J. Rogers Kniffen Worldwide Enterprises.
Wal-Mart's global Internet sales rose 30 percent last year, while Amazon registered sales growth of "only" 20 percent, The Wall Street Journal reported, citing data from trade publication Internet Retailer.
"Once Wal-Mart gets to the point where Macy's is … they're going to be a fierce threat to Amazon," he argued.
"I won't buy Amazon," Kniffen explained.
Wal-Mart is scheduled to report first-quarter earnings Thursday. The consensus estimate among Wall Street analysts calls for profit of $1.15 a share. Kniffen said he doesn't see Wal-Mart beating expectations.
But Kniffen said he's still a "big fan" of the retailer and would buy its stock, though he doesn't own it himself.
Going forward, Wal-Mart should benefit from the trend of increasing "disposable personal income" among consumers.
—By CNBC's Matthew J. Belvedere.