Defensive linemen Dre’Mont Jones and Nick Bosa have already announced they will enter the draft, as has running back Mike Weber, while linebacker Malik Harrison told reporters in the locker room after the Rose Bowl he will return.
Among the group of players still considering his options are star quarterback Dwayne Haskins and All-American center Michael Jordan.
Fuller and Harrison shared the team lead with 81 tackles in 2018.
Fuller had an interception, broke up four passes and recovered two fumbles.
Fuller’s announcement came the same day fellow Big Ten East division contender Penn State has lost its fifth player to early entry in the 2019 draft.
Nittany Lions running back Miles Sanders joins offensive linemen Ryan Bates and Connor McGovern and defensive linemen Kevin Givens and Shareef Miller.