The move comes as no surprise, given that Scrubb suffered an ACL tear and is expected to miss the season.
Scrubb, 23, is 6-foot-5 and has spent his time in the NBA on two-way or non-guaranteed contracts, appearing in two games with the Magic last season and 22 combined in two years with the Clippers before that.
The No. 55 overall pick in the 2020 NBA Draft, Scrubb signed a two-way deal with Boston on July 15.
Meanwhile, Knight joins shooting guard JD Davison and center Neemias Queta as the Celtics’ two-way players entering the season.