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Cowboys center Travis Frederick has been out of practice recently, and today he revealed why: He has been diagnosed with Guillain-Barré syndrome, a rare neurological disorder in which the body’s immune system attacks the peripheral nervous system.

Frederick released a statement saying he does not know when he will return to the field.

“After a very extensive examination and discovery process over the past few weeks, I have been diagnosed with having Guillain Barre Syndrome which is an auto immune disease,” he said. “In the last 48 hours, I have received two treatments that address my condition, and I am feeling much better from an overall strength perspective. I will continue these treatments over the next few days. I am very optimistic about my condition and the immediate future, as I have been told that the illness was detected at a fairly early stage. My doctors have told me that it is not possible to determine a time table for a return to the field right now, but I am hopeful that I will be able to play as soon as possible. I am deeply grateful for all of the people who have expressed concern for me throughout the past four weeks, and my teammates and the Cowboys organization have provided me and my family with tremendous support.”

Frederick has started all 16 games in all five seasons since the Cowboys drafted him in 2013.