Dallas ? Former Dallas Cowboys running back Ron Springs has been hospitalized in a coma, more than seven months after receiving a kidney donated by ex-teammate Everson Walls.

The Washington Redskins said Tuesday that cornerback Shawn Springs, son of the 50-year-old Springs, had left the team to be with his father.

“(Shawn) has flown down there – it’s a very tough time for them because I think it’s very, very serious,” Redskins coach Joe Gibbs said.

It wasn’t immediately clear what caused Ron Springs, who has diabetes, to lapse into a coma or when he was hospitalized. Calls to the family weren’t returned.

In February, Walls donated his kidney to the ailing Springs, who had suffered from diabetes for 16 years and had been on the national transplant waiting list since 2004. It was the first transplant between two former U.S. professional athletes.

The disease confined Springs to a wheelchair and led to the amputation of his right foot and the big and middle toes on his left foot.

In an August interview with the Associated Press, Springs said he could feel his health improving each day since the transplant.

“I’m feeling very good,” he said at the time. “Every day I get a little bit better.”

Springs played eight seasons in the NFL, six with the Cowboys and two in Tampa Bay, before retiring after the 1986 season. He was drafted in the fifth round by the Cowboys out of Ohio State.

In the four seasons Springs and Walls played together in Dallas, the two forged a strong friendship. Springs is the godfather of Walls’ oldest daughter, and Walls received the same honor for Springs’ youngest.

This summer, Ron and Shawn Springs visited several cities in a campaign to increase awareness of diabetes.