Johnson was not one of the 34 selected to take part in minicamp, but, because he lives close by, he along with Elfrid Payton, Arron Afflalo, Terrance Jones and C.J. Watson will take part in the scrimmage portion.
The C's big man will be on the Blue Team that includes Bradley Beal, Harrison Barnes, DeMar DeRozen, Andre Drummond, Kenneth Faried, Rudy Gay, Victor Oladipo and Elfrid Payton.
This is an unexpected treat for Celtics fans who can watch their newly signed big man play against some of the leagues elite.