Frederick said he was diagnosed with the disease after exhaustive tests conducted over the past few days. He has received treatments over the past 48 hours.
"I am feeling much better from an overall strength perspective," Frederick said in a statement Wednesday. "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."
According to the National Institute for Neurological Disorders and Stroke, Guillain-Barré causes the body to attack a network of nerves around the brain and spinal cord. Most people recover from even the most severe cases of the disease, but some will continue to have some degree of weakness, according to the institute.
Frederick said doctors have told him there is no timetable for his return. However, it is possible he could miss multiple weeks of the season, sources said.
"I am hopeful that I will be able to play as soon as possible," Frederick said.
Frederick has not missed a game in the first five years of his career and has been named to the Pro Bowl the past four seasons.
Last week in California, Frederick was examined by neck specialist Dr. Robert Watkins after having symptoms similar to that of a stinger. With the weakness not subsiding when the Cowboys returned to Dallas, Frederick met with more specialists in Dallas, and the diagnosis of Guillain-Barré syndrome was determined through blood work.
"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 said.
With Frederick out, Joe Looney will start at center.
The Cowboys also enter their Sept. 9 opener at the Carolina Panthers uncertain about the availability of Pro Bowl right guard Zack Martin, who injured his left knee in last week's preseason game against the Cincinnati Bengals, but he and the team are hopeful he can play in Week 1.
The Associated Press contributed to this report.