He should learn how to handle his money well. He can start by limiting his budget in gambling. Take only few percentage on his salary. He can still even gamble with small amount of set budget. Atleast, this way, it will not hurt much his budget or salary. He can control his finances well. He can also get saving account to put his money. He can also try taking break from gambling. Try to make him realize what he is facing right know to enlighten himself. If you think these cannot help him, or he cannot help himself, then it's much better for him to seek professional help.
Not many people wants to learn how to handle their money well because if that person getting inside gambling, he will forget about everything needs to do in gambling. Playing gambling can makes him tempts to comes back over and over until his money is gone while he will not realize about that. Limiting his budget in gambling is the important things that he can do to prevent the big lose and spends much money in gambling. If he can do that, he will not lose much money and only use the money he can afford. He can handle his finances well while he will allocate some money to playing gambling and always remember about his rules while playing gambling. It's better if he can research what he needs to do to playing gambling so he can be aware about the risks.