Watch out Amazon! Wal-Mart is coming: Retail pro

Retail sales on display
Retail sales on display

Wal-Mart is fast becoming a "fierce threat" to Amazon's dominance of online shopping, a leading retail analyst told CNBC on Wednesday.

"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.

Read MoreMacy's sales fall as weather keeps shoppers away

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.

Jin Lee | Bloomberg | Getty Images

Wal-Mart is moving "very aggressively" into the in-store and online, omnichannel, retail space, Kniffen said in a "Squawk Box" interview. "The same place Macy's is. Same place that Nordstrom's is."

Read MoreSears eyes selling some or all of Sears Canada

"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.