Dallas Cowboys center Travis Frederick announced on Wednesday that he's been diagnosed with Guillain-Barre Syndrome, an autoimmune disease, and that doctors told him "it is not possible to determine a time table for a return to the field."

Frederick has received two treatments in the past 48 hours to address the condition and said he's feeling much better. He met with a specialist on Monday regarding what was then thought to be a neck stinger.

The four-time Pro Bowler was signed to a six-year, $56.4-million extension in 2016 after being named an All-Pro.

For now, at least, Frederick joins Cowboys guard Zack Martin on the sideline. Martin was initially diagnosed with a hyperextended left knee, but he's expected to be ready for Week 1 after the team announced he avoided significant injury.