Junior Galette has suffered a torn Achilles and will be out for six to eight months.
Galette's injury happened at the end of Wednesday's practice.
Jay Gruden didn't confirm the Achilles tear but told reporters earlier Wednesday that Galette suffered a left ankle/foot injury.
"I'm very concerned," Gruden said.
Galette, 27, was released by the New Orleans Saints earlier this summer, less than a year after they signed him to an extension worth up to $41 million.