We introduced a new cat into our household and it isn't really eating?

[Evilteenietiff]

Three days ago I had a new housemate move in. He has a male rag doll semi long hair cat. Desexed. He is around 4 years old.

I already had a female desexed long hair cat. The two don't really seem to get along too well at the moment, we have introduced the two slowly, only recently have they been in the same room as each other.

The problem is that Moon-Unit, the male cat who has moved in with us isn't really eating or drinking much. Any suggestions?
He also has his own food and water bowls and his own litter tray. Thank you for the suggestions thus far