DALLAS — Former Dallas Cowboys running back Ron Springs, who spent the past four years in a coma after losing oxygen during a 2007 operation, has died without ever regaining consciousness. He was 54.

Former Cowboys teammate Everson Walls, who donated a kidney to Springs for a transplant, says the Springs family informed him that his friend died about 4:30 p.m. Thursday at Medical City Dallas hospital.

The hospital is where Springs first slipped into the coma in 2007 after undergoing surgery to remove a cyst from his forearm about seven months after receiving the kidney.

In 2008, Springs’ wife, Adriane, filed a medical malpractice lawsuit against two doctors she says caused brain damage to her husband during the cyst surgery.

Despite the lengthy coma, the death came as a surprise, Walls said.

Springs was drafted by the Dallas Cowboys out of Ohio State in 1979 and became a starter alongside Tony Dorsett in ‘81, the year Walls arrived as an undrafted rookie from Grambling. Springs left in 1985, finishing his career with two seasons in Tampa Bay.

He ran for 2,519 yards, had 2,259 yards receiving and scored 10 touchdowns in his NFL career.