Give some more details as to what is going on...like, was he eating and suddenly stopped? Is he swimming a breathing ok, or abnormally? water conditions / quality? Other tank inhabbants and any signs of agression? ETC??
Some fish acclimate slower, give him 2 days, if still not eating or his breathing has not improved remove him. Clowns are very easy to feed, they should eat everything. Check with who you bought the fish though to see what he was eating
