One method, if you want it to fade in in relation to the player, is to set the opacity of the object depending on the distance between object and player.
So, set object opacity to 100-(distance(player.x,player.y, object.x,object.y*0.1)) for example.
This way its visibility will always be in relation to distance, instead of just fading all the way in or all the way out. Not sure if you want this, but just thought I'd give an idea :)