FRISCO, Texas -- Dallas Cowboys Pro Bowl center Travis Frederick announced his retirement via Twitter on Monday.

The move came as something of a surprise to the Cowboys, but sources said there had been rumblings that Frederick, who just turned 29, had been contemplating walking away.

In his announcement, Frederick made reference to his battle with Guillain-Barré syndrome, an autoimmune disease that affects the nervous system, which knocked him off the field in 2018. Frederick lost strength and some motor skills but was cleared to return last year and started 16 games.

Numerous times throughout his recovery, Frederick said his goal was to not just return to the game but continue to play at the highest of levels. Frederick said in his statement he considered retirement as he battled GBS, but could not walk away without getting back to football.

"I made my return to the field, played well overall, and was selected to the Pro Bowl, but it was a difficult year for me," Frederick said in his announcement. "Each day I faced a struggle: I could no longer perform at my highest level. Playing 'well' is not what I expect of myself and is not what my teammates deserve. Because of this, I know my days as a football player are done. I am proud of what I have accomplished in my career, and I walk away with my head held high."

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— Travis Frederick () March 23, 2020

The Cowboys selected Frederick in the first round of the 2013 draft, No. 31 overall, and he started every regular-season game (96) he played, as well as three playoff games. He was named to the Pro Bowl in 2014-17 as well as 2019 and was a first-team All-Pro pick in 2016.

"Travis Frederick, by the nature of his center position, was the core piece of what I believe to be one of the most talented and skilled NFL offensive lines that has been assembled," Cowboys owner and general manager Jerry Jones said in a statement. "His leadership ability, production and intelligence put him at the top level of interior offensive linemen in our league for many years. At the pinnacle of his success, his career on the field was only exceeded by a rare display of courage and determination in overcoming a life-threatening illness and returning to the game -- a challenge that could only be completed by a person with rare levels of perseverance and strength."

The Cowboys signed Frederick to a six-year, $56.4 million extension before the 2016 season that included $28 million in guaranteed money. In theory, the Cowboys could look to recoup signing bonus money because of his retirement announcement.

Last week, the Cowboys signed Frederick's backup, Joe Looney, to a one-year deal worth $2.4 million. Looney started every game in Frederick's absence in 2018 and performed well. The Cowboys also have Adam Redmond under contract as a potential backup, and it is possible Connor Williams, who has started most of the past two seasons at left guard, could get some work at center after he returns from a torn anterior cruciate ligament he suffered late last season.

The Cowboys also have last year's third-round pick, Connor McGovern, who did not play a snap because of a pectoral injury, as an option. He played center at Penn State for a season.

Through his Blocking Out Hunger Foundation, Frederick has in recent days been focused on aiding children's access to food during the COVID-19 crisis that has closed schools for an extended amount of time. Along with some teammates and coaches, Frederick pledged to match up to $40,000 in donations, noting that $2 feeds a child for a day and $25 feeds a child for two full weeks.

"Travis is an incredible player, teammate and leader, who inspired us with his work ethic and perseverance, especially after knowing what he went through in 2018," Cowboys linebacker Sean Lee told ESPN. "To go from having trouble walking to the Pro Bowler he is, was just incredible to watch. His play on the field and his dedication to helping the community was second to none and he'll be dearly missed. I'll miss him in the locker room and competing against him in practice, but I know he's excited for what's next in his life and I'm happy for him."

In 2017, Frederick was the Cowboys' nominee for the Walter Payton Man of the Year award.

"As a contributor to our community, a family man and a professional person, he has distinguished himself as an exemplary representative of this organization," Jones' statement continued. "And for the rest of his life, when his name is mentioned in the same sentence with the Dallas Cowboys, he will be lifting the standards of excellence and esteem that has characterized the history of our proud franchise."