Plavsic graduated from Hamilton Heights Christian Academy in Chattanooga, Tennessee, before redshirting with Arizona State last season. He is originally from Ivanjica, Serbia, but moved to the United States in October 2017.
"He a strong, physical player who can hold his own in the paint, and his offensive skill set could allow him to play away from the basket, keeping the floor spaced," Tennessee coach Rick Barnes said in a statement Tuesday.
Plavsic plans to enroll at Tennessee for the first session of summer school.
Tennessee said Plavsic will seek an NCAA waiver that would enable him to play for the Volunteers immediately. If he isn't granted a waiver, he would have to sit out the 2019-20 season.