I am not certain there is much you can do , perhaps try to make him strong in himself ,let him join sports clubs or outside activities to build his self esteem ,not certain where you are from but in the US we have many after school clubs, outside games and sports are great for children like him, ask his teacher if there is anything he can be part of. Dont make much issue about his friends let him feel his own way in the matter.,the more he pushes the quest the more they may push back, if he stays in the back ground and is himself, and doesnt seem too alone they may find him interesting.Make it your quest to brighten him up and make him less needy ..good luck