Dwight Clark, right, with fellow 49ers legend Joe Montana at Candlestick Park in San Francisco in 2011. (Thearon W. Henderson/Getty Images)

Former San Francisco 49ers wide receiver Dwight Clark, best known for making “The Catch” in the 1981 NFC championship game, announced Sunday that he has been diagnosed with amyotrophic lateral sclerosis (ALS).

“In September of 2015, I started feeling weakness in my left hand,” Clark wrote in a statement. “I was mildly paying attention to it because since my playing days, I’ve constantly had pain in my neck. I was thinking it was related to some kind of nerve damage because it would just come and go. After months of tests and treatment, I got some bad news. I was diagnosed with amyotrophic lateral sclerosis. I have ALS, also known as Lou Gehrig’s disease. Those words are still very hard for me to say.”

Clark, 60, said he was diagnosed with the disease after visits to six neurologists and three ALS specialists.

“The one piece of good news is that the disease seems to be progressing more slowly than in some patients,” Clark wrote. “While I’m still trying to wrap my head around the challenge I will face with this disease over the coming years, the only thing I know is that I’m going to fight like hell and live every day to the fullest.”

Clark said he has started experiencing weakness in his right hand, abs, lower back and right leg.

“I’ve been asked if playing football caused this,” Clark wrote. “I don’t know for sure. But I certainly suspect it did. And I encourage the NFLPA and the NFL to continue working together in their efforts to make the game of football safer, especially as it relates to head trauma.”

Clark tweeted a link to his statement Sunday night. His Twitter avatar is the iconic image of him leaping to pull in Joe Montana’s pass with 58 seconds remaining in the NFC championship at Candlestick Park on Jan. 10, 1982. Clark’s grab, which came to be known simply as “The Catch,” helped the 49ers defeat the Dallas Cowboys, 28-27, and clinch a spot in their first Super Bowl. Two weeks later, the 49ers defeated the Bengals, 26-21, in Super Bowl XVI.

“What I love about it the most is that it’s connected me with 49ers fans for the rest of time,” Clark said of ‘The Catch’ in 2013. “I didn’t realize at the time that people would keep talking about it. But they not only talk about it, they pass it down through the generations. I’ll be at an autograph thing, there’ll be a 10-year old kid saying, ‘You’re The Catch.’ ”

Clark, who played all nine seasons of his career with the 49ers, thanked his friends for their support and released a series of remarks from his former teammates about his diagnosis.

“Jennifer and I are saddened by the diagnosis of Dwight,” Montana said, via the Mercury News. “This is a difficult time for Dwight, Kelly and all of us who love him. He is family, and in our continual thoughts and prayers. We hope the public will be cognizant of Dwight’s desire for privacy.”