This comes two days after head coach Jeremy Pruitt was fired amid an investigation into what UT chancellor Donde Plowman said were "serious NCAA rules violations."
Assistant coaches Brian Niedermeyer and Shelton Felton also were fired, along with four members of the on-campus football recruiting staff, the director and assistant director of football player personnel and a football analyst/quality control coach.
Kevin Steele, who was hired as an assistant coach on Jan. 12, was named interim head coach after Pruitt's firing.
To'o To'o, a sophomore, started all 10 games this past season and led the team with 76 tackles and 10 tackles for loss. A former four-star prospect from California, he signed with Tennessee in 2019 over Alabama, Utah, USC and Washington.
Crouch, a sophomore from North Carolina, started every game this past season and finished third on the team in tackles with 57.
Gray, a sophomore from Memphis, emerged as one of Tennessee's best backs in 2020, ranking sixth in the SEC in rushing yards per game (85.8) and sixth in yards from scrimmage per game (114.0).
Johnson is a redshirt senior, but he can make use of the NCAA's decision to grant an extra year of eligibility to fall and winter sports athletes.