It's often difficult fitting in to a new team. Maybe, he needs to be approached more, brought in more by other team members. Not just in business conversation, but in more personal or non business talk. By doing this, he may begin to feel 'accepted' and a more vital team member.
We have a large team (30+folks) and I've had new people comment that they felt like there were 'clicks' or at least there were 'perceived clicks' and they didn't feel welcome. It wasn't intential, it simply takes 'intentional thought' to include others in our conversations when we don't know them as well.