Privately held Chick-fil-A is not just growing fast, it’s becoming a growing threat to a number of large publicly held chains, including the biggest of them all, McDonald’s Corp.

According to Kalinowski Equity Research, Chick-fil-A could move into the number three spot on the list of largest U.S. restaurant concepts in 2018, which was held by Subway, the privately held sandwich chain, in 2017. That would be ahead of the 2020 projection made by others.

Kalinowski cites Restaurant Business data^[1] that shows Chick-fil-A sales up 15.5% this year. Traffic is up 10%.

In 2017, Chick-fil-A’s U.S. systemwide sales were $9.021 billion, up 14.2%. In 2018, that sales total could near $10.4 billion.

“We have long pointed out that Chick-fil-A is the restaurant competition with which McDonald’s U.S. should most concern itself – and by extension, investors should too,” the note said. “But this goes beyond McDonald’s.”

McDonald’s MCD, +1.14%^[2]   was the top concept in 2017 with U.S. systemwide sales of $37.6 billion. Starbucks Corp. SBUX, +0.43%^[3]   was in the number two spot with $17.65 billion in U.S. sales.

Read: What McDonald’s can learn from Chick-fil-A and Subway^[4]

“If this plays out this way, Chick-fil-A’s 2018 U.S. systemwide sales would easily surpass those of Burger King and Wendy’s,” Kalinowski wrote. Burger King is part of the Restaurant Brands International Inc. QSR, +2.04%^[5]   portfolio.

In notes published earlier this year, Kalinowski highlighted just how large McDonald’s chicken business is, with the company selling more pounds of chicken than beef in 2011.

But Chick-fil-A has plenty of room to grow. For example, as of March 2018 Chick-fil-A only had 11 restaurants in New York, a state with more than 19 million residents, according to Kalinowski. Other states, including Massachusetts, Ohio and New Jersey, could also add locations, and market share at other chains’ expense.

See: McDonald’s to trim antibiotics from its beef^[6]

Wendy’s Co. WEN, +0.97%^[7]   , and the chicken sandwich business it has built, could also be in the crosshairs.

“For years – decades – Wendy’s has received credit from the consumer for offering chicken sandwiches that are higher in...