Chris Johnson, a former first-round pick of the Tennessee Titans and Pro Bowl running back, revealed he has been diagnosed with ALS, also known as Lou Gehrig's disease. Johnson told "Good Morning America" that he was officially diagnosed last year. Johnson is 40 years old. 

"There's no history of ALS in my family," Johnson told co-anchor Michael Strahan in an interview aired on Monday." "My doctors believe my case is what's called sporadic ALS, which is actually how the vast majority of ALS cases happen."

Johnson noted that he was feeling good last year and was working out daily, while spending time with his wife and four children. However, he started to feel weakness in his right hand, and while his wife, Brittany Johnson, thought it could be a football-related injury like a pinched nerve, it was ALS taking shape.  

"I first noticed weakness in my right hand," he said. "At first, it was little things like my grip didn't feel right and I wasn't as strong as I've always been."

Johnson said the news of his diagnosis came as a "shock." He relayed that the doctor who delivered the diagnosis said a medication could extend his life by a few months and that he and his wife should "get our affairs in order." There is no known cure for ALS. 

"Honestly, I don't know if you ever fully process it," Johnson said. "At first, you're in shock. Then you realize you have two choices. You can give up, or you can fight. I chose to fight."

The disease has progressed rapidly for Johnson, who now uses a speech-generating device to communicate. He recorded his voice following his diagnosis so that his device delivers a voice that sounds like his own. 

"It's continued to progress much faster than I ever imagined. I want people to understand just how quickly ALS can attack your body," he said. "Just over a year ago, I was picking up my 7-year-old daughter so she'd make a wish with her birthday cake. Today, I couldn't do that."

Johnson said that he wants to not only raise awareness of ALS, but told "GMA" that he also wants to convey that he is still the same person they remember as a star running back in the NFL, who once rushed for over 2,000 yards in a single season. 

"I want people to know that I'm still me. ALS has changed what my body can do, but it hasn't changed who I am," he said. "People sometimes look at the physical disability and assume you're not still the same person inside. I still think the same. I still dream. I still love my family. My body just doesn't cooperate."

Titans statement on Chris Johnson's ALS diagnosis

Amy Adams Strunk, controlling owner of the Titans, said in a statement that learning of Johnson's diagnosis was "extremely difficult" and that the back left "mark on an organization that you just can't put into words." 

You can read the full statement below: 

"Some people leave a mark on an organization that you just can't put into words. Chris Johnson is one of those people for us. His leadership on the field, in addition to his impact in the locker room and Nashville community have written him permanently into the story of this franchise.

"Learning this news is extremely difficult, and we will support Chris every step of the way throughout his journey. We are holding him and his family close, and join our fans around the world in expressing our love for Chris."

Full 'Good Morning America' interview

The full interview with Chris and Brittany Johnson with "Good Morning America" co-anchor Michael Strahan can be watched below.

Remembering Chris Johnson's playing career

Johnson entered the NFL as the 24th overall pick of the Titans during the 2008 draft out of East Carolina. The Florida native burst onto the scene, totaling 1,488 yards from scrimmage and 10 total touchdowns as a rookie. 

In 2009, Johnson became the sixth of just nine players to ever rush for over 2,000 yards in a single season. He also broke Marshall Faulk's single-season record for scrimmage yards with 2,509. That earned him the nickname "CJ2K" and Johnson was also named Offensive Player of the Year that season. 

Johnson played six seasons for the Titans and currently ranks fourth on the franchise's all-time rushing yards list. Over his tenure, he was named to the Pro Bowl three times (2008-2010) along with his first-team All-Pro nod and Offensive Player of the Year award for that spectacular 2009 campaign. 

Johnson last played in the NFL in 2017 as a member of the Arizona Cardinals. He also spent one year with the New York Jets in 2014. 

For his career, the back totaled 9,651 rushing yards and 55 rushing touchdowns, while adding 2,255 yards receiving and nine receiving touchdowns on 307 catches. He appeared in 130 regular-season games.