Devon "Rockhead" Johnson, a standout running back at Marshall University who had signed with the Carolina Panthers as an undrafted free agent for the 2016 season, died suddenly on Tuesday. He was 25.

According to a report by Grant Taylor of The Herald-Dispatch, Johnson died abruptly of an undisclosed cause at Bluefield Regional Medical Center in Bluefield, West Virginia.

"I am shocked and saddened at the news of Devon Johnson’s passing," said Marshall Thundering Herd head coach John Doc Holliday in a statement released Tuesday evening. "Devon was a force in our program, both literally and figuratively.

"Whether on the field or off, his impact was immeasurable and he will be missed by so many at Marshall. Our thoughts and prayers go out to his friends and family."

Enrolling at Marshall in 2012, Johnson went on to have an outstanding career with the Thundering Herd, standing out as part of the team's 2014 Conference USA Championship Team and running for 1,767 yards, including a school record 272 yards in a single game against Florida Atlantic. He was named First-Team All-Conference USA, and was a semifinalist for the Doak Walker Award, given to the top running back in college football.

After averaging a school record 7.8 yards per carry during his college career, Johnson went undrafted in 2016, and signed with the Panthers shortly afterwards as a fullback. However, Johnson would spend his entire rookie season on Injured Reserve, and was released by the team in May of 2017.

"Devon was an incredible football player, but an even better person," wrote Johnson's family in a statement shared by Joe Person of The Athletic. "He forged and treasured relationships from childhood, to his success as a member of the Marshall Thundering Herd, to his time spent in the Carolina Panthers organization, and beyond.

"Devon will always be in our hearts, and we sincerely appreciate the outpouring of support, thoughts, and respects."

The Johnson family has requested privacy in their time of mourning. As of Tuesday night, the Panthers have yet to issue a statement on Johnson's passing as they prepare to travel to Pittsburgh for their Week 10 game against the Steelers.

Johnson was part of an undrafted free agent class for the Panthers that included tight end Jake McGee, linebacker Jared Norris, wide receiver Keyarris Garrett, running back Andrew Bonnet, wide receiver Jenson Stoshak, and safety Jeremy Cash. Of those signings, only Norris remains with the team. McGee and Cash remain in the NFL, but both are on the Injured Reserve list of their respective teams (McGee with the Pittsburgh Steelers and Cash with the Arizona Cardinals).

For his final career statistics at Marshall, Johnson had a total of 2,373 rushing yards, 423 receiving yards, 29 tackles, and 31 touchdowns. Funeral arrangements are pending.