Marion Barber, a former NFL running back who played for the Dallas Cowboys in the 2000s and was 38 years old, died Monday after being discovered by authorities in Frisco, Texas, during a wellness check. Barber was an outstanding running back for the Dallas Cowboys in the 2000s. A cause of death has not been disclosed yet.

After his NFL career, Barber’s life was marked by struggle, including worries about his mental health and encounters with police in the Dallas metro area. Dez Bryant, a former teammate of Barber’s who stated last summer that he couldn’t enjoy watching archived footage of his playing days knowing what he had gone through after his NFL career, is among those mourning him.

“RIP Marion Barber may God rest your soul,” Bryant tweeted. He also had a message for athletes in a video, urging them to look out for themselves while noting the deaths of other NFL players such as Demaryius Thomas and Vincent Jackson, who both died in their 30s.

Frisco police were dispatched to an apartment they believe Barber was renting, according to a department representative. When cops entered the building, they discovered Barber’s body. An investigation into “an unattended death at the location” is now underway in cooperation with the coroner’s office.

Barber’s trademarked running style, which earned him a legion of fans during his career, made him a favorite among spectators, and his coaches frequently called on him to score drives by fighting his way through tacklers and into the end zone.

In his third year, Barber led the Cowboys with 10 touchdowns and made the Pro Bowl despite never being named a starter. Only three players in Dallas history have scored more points than Barber’s 47 rushing touchdowns.

The team issued a statement expressing its sorrow at Barber’s death.

“Marion was an old-school, hard-nosed football player who ran with the will to win every down,” it said. “He had a passion for the game and love for his coaches and teammates. Our hearts go out to Marion’s family and friends during this difficult time.”

Barber, who was a fourth-round selection of the Dallas Cowboys in 2005, played seven seasons in the NFL, including six with the Cowboys and one with the Chicago Bears. He retired after the 2011 season.