Shares of McDonald's slipped this morning after the global fast-food giant, which controls roughly half the U.S. hamburger chain market, reported lower than expected sales and profits, and projected a "relatively flat" summer, as Mark Kalinowski, fast food analyst at Janney Capital Markets in Philadelphia, told clients in a report this morning.

"We believe one reason for this is a resurgent Wendy’s," writes Kalinowski. "In the U.S.. Wendy’s recently-launched Pretzel Bacon Cheeseburger appears to be on track as the best-selling new product introduction by that burger concept in at least a decade. This pressure on McDonald’s could last over the third quarter as a whole, and perhaps beyond, if Wendy’s adds its Pretzel Bacon Cheeseburger as a permanent menu item – which looks increasingly likely."

Wendy's, which recently topped Burger King as the No.2 U.S. hamburger chain (though still far behind Mickey D), could come off a "so-so" Spring to report third-quarter sales up a big 5%, Kalinowski writes. His poll of McDonald's franchisees show many are so far unimpressed by their company's recent healthier but smaller product offerings.