I'd say a poor man's Rudy Gay.
Rudy Gay is the name that comes to my mind as well, although I'm not so sure Jeff Green is worse than Rudy Gay. Not this year, at least.
Rudy is a better rebounder and a slightly better FT shooter, but that's about it. Jeff Green is a better deep shooter, a more efficient scorer overall, less turnover-prone and a better defender. Rudy scores more points, but only because he takes more shots.
Given a choice between them, I'd take Jeff Green.