My clowns have been in my tank for months and they also rarely come out from their right back corner. lol
Just give him some more time to adjust, he'll eventually come out a bit more I bet. Is the clown eating and does it look ok?
180g- Mostly BIG fish and some coral. ~80g Nuvo- My coral tank with "happy fish"~ 90g- FOWLR Not the not happy type of fish~ 125g- Freshwater Malawi Cichlids ~10g- Nuvo- The refugees from the Ich of '18