SAN FRANCISCO—Former SF 49ers wide receiver and general manager Dwight Clark, 60, shared on Sunday, March 19, that he has amyotrophic lateral sclerosis (ALS), which is also known as Lou Gehrig’s disease. It is a disease that affects the neurons which control voluntary muscles.

Clark, who played for the 49ers from 1979 to 1987 (winning two Super Bowls during his career), disclosed information on his illness on former 49ers manager Eddie Debartolo’s website.

In September 2015, Clark began to experience weakness in his left hand, which he seldom acknowledged. He suspected nerve damage that would “just come and go.”

Clark wrote in his letter that he has now lost strength in his right hand, back, abdominals, and right leg. He wrote that tasks such as “opening a pack of sugar or buttoning my shirt” are “impossible.”

“I can’t run, play golf or walk any distances. Picking up anything over 30 pounds is a chore.” He added: “The one piece of good news is that the disease seems to be progressing more slowly than in some patients.”

People have asked Clark whether or not he believes that football was the primary cause of his condition and is motivating the NFL and NFLPA to work in tandem to make football safer, especially in regards to head trauma.

ESPN said that ALS has been linked to chronic traumatic encephalopathy, a degenerative brain disease that research studies have connected to people with a history of head trauma, such as concussions. SF 49ers CEO Jed York shared that he was “deeply saddened” upon hearing about Clark’s illness.

“Many know Dwight as an iconic figure in 49ers lore, whose accomplishments on the field brought joy to fans around the world. Our organization is fortunate to know him more intimately as a wonderful man who has given so much of himself as an ambassador to the entire Bay Area. We will stand alongside Dwight and his family as they wage this battle,” York disclosed.

John Lynch, the 49ers general manager, also shared his thoughts upon hearing of Clark’s diagnosis:

“My family and I were truly saddened by Dwight’s announcement. Three years ago, our family lost my mother-in-law to this heartbreaking disease. During her battle, we found strength and comfort in the support of hose who loved her. Now, I urge 49ers fans, fans of football, to band together and join Dwight and his family’s fight against ALS.”

One of Clark’s most notable NFL plays was known as “The Catch.” In the 1981 NFC Championship game against the Dallas Cowboys, Joe Montana threw the ball to Clark, who was standing at the back of the end zone. Clark made the reception and scored the winning touchdown.

His career record stands at 506 catches for a total of 6750 yards and 48 touchdowns.