In another Indiana twist, Lee played at Pike High School in Indianapolis before playing at Western Kentucky University.
Lee averaged 11.4 points in 30.3 minutes per game last season and shot 40.1 percent beyond the 3-point arc in 58 appearances, including 26 starts.
Johnson, Moore and Williams all were absent from the Celtics' summer league game in Las Vegas against the Sacramento Kings on Thursday.
ESPN reported that Johnson was never seen in the arena, while Moore and Williams arrived with the team but eventually left the floor during warm-ups. Moore and Williams each shared a one-on-one conversation with Celtics coach Doc Rivers in the tunnel next to Boston's locker room before departing the arena.