The upcoming menu addition was discussed during the fast-food giant's turnaround summit in Las Vegas last week, a source familiar with the meeting told CNBC.

"Possibilities include kale for use in salads, or perhaps a kale smoothie," wrote Janney analysts in a note to clients. "More generally, McDonald's clearly aims to raise consumers' perception of the quality of its food. Adding kale to the menu in some way could help be a step in this direction."

McDonald's will debut kale as an ingredient in the not-too distant future as the fast-food giant continues its efforts to adapt to changing consumer preferences, according to a recent note from Janney Capital Markets.

It is the latest sign that McDonald's is committed to more change in its struggling U.S. unit. Last week week, it vowed to switch to sourcing chicken raised without human antibiotics within the next two years. It also plans to offers customers milk from cows that are not treated with rbST, an artificial growth hormone.



McDonald's declined to comment on the kale menu addition in an email to CNBC.

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"We're always looking at new and different ingredients that customers may enjoy," spokeswoman Lisa McComb said in an email, adding the chain doesn't "comment on content from internal meetings so there's nothing to share."

Late last year, McDonald's USA President Mike Andres stressed the need for changing domestically and told investors its pace of change internally has lagged that outside the company. He noted "consumers have redefined quality and value" with a bigger focus on wellness.

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One franchisee's director of operations said adding kale was a good move for McDonald's, which continues to battle negative trends domestically.

"We're here to give what our customers want," he said. "If that's what our customers want, we'll give it to them."

"The last 10 years, we could have evolved quicker than we have," he added.