Do the Celtics need Jabari Parker? Enes Kanter and Dennis Schroder can fill the instant offense off the bench role. Juancho Hernangomez is another body who can be a backup four.
As the only player on the roster with a contract that is not fully guaranteed, Parker seems like the obvious player you cut if you have a way to upgrade the roster, especially since he doesn't seem like a great fit for what the Celtics look like they are trying to do. But what upgrades are desirable?
If I were to pick one role player skill that I would like to see the Celtics acquire, it would be someone who can serviceably defend big wings. Right now, only Jayson Tatum and Jaylen Brown seem suited to that task. Otherwise, you're relying on a bunch of bigs who might be able to not be a disaster for a possession or two if switched, but who shouldn't be tasked with guarding a wing full-time. I'm not sure who is available, though. There's not much on the free agent market. The closest fits might be Rondae Hollis-Jefferson and maybe James Ennis III. Maybe there's a veteran available for trade using a trade exception, but that player is likely to be either overpaid of not very good, given the relative scarcity of wings. Maybe there is a player who would be a final cut by another team who makes more sense on the Celtics than Parker.
What sort of player would you be looking to give Jabari Parker's roster spot to if the Celtics to fill it with someone who is a better fit for the team concept?