Walmart isn't yet sure how much of a hit it will take because of the deadly coronavirus outbreak that started in China and has now spread across the globe. But it will likely take one.

"It's not in our guidance," CEO Doug McMillon told CNBC's Courtney Reagan on Tuesday morning, on the heels of the retailer reporting its fiscal fourth-quarter and full-year results.

"It's too difficult to tell at this early stage exactly how to forecast it," he said about the coronavirus. "We are still operating our stores [in China]. Almost all of them are open ... but operating on reduced hours," with a focus on selling food and consumables, he said.

Walmart has 430 locations in China. It also has a minority stake in JD.com, one of China's leading e-commerce players.

"Shipping and product coming out of China ... into the U.S. ... is an issue," McMillon said. "It's too difficult to call right now exactly what will happen in the [first] quarter. But we've said, because of what's happening on the ground in China ... we do expect to have some impact. But we are not currently putting that into our guidance."

Looking to full-year fiscal 2021, Walmart said Tuesday that it is calling for earnings to fall within a range of $5.00 to $5.15 a share. Analysts had been calling for annual earnings of $5.22 per share.