hello soodyogesh
my apologies for responding so late...
With regards your query, my opinion is that you possibly have arotator cuff problem. this is a common injury with sports that involve overhead activities, by over head i mean sports that involve you raising your arm literarilly above your head i.e tennis, javelin, short put, volleyball...
this again happens when the stability in your shoulder is not optimal , with tennis/volleyball, the force of the ball on the racket/hand and the position of your shoulder are in opposite directions..if your shoulder joint complex is not optimal as you would have it with the wrong technique of smashing, then you could have too much anterior displacement of the humeral head within the joint, this can cause some trauma to the capsule as well as the rotator cuff muscles..
my guess is you naturally have an anteriorly displaced humeral head naturally. This means that (and im only speculating from your description of your mechanism of injury) your arm bone head lies too much infront of the joint either because things are too tight at the back or you have certaim structures within your shoulder joint being too shortnaturally pulling the head in the position.
With regards whether this may be a problem in the future, its hard to say, it probably will lead to some early joint changes what we call arthritis (if the problems are not corrected and you keep pushing it through its limits) because it this does not heal properly then there would be compensations happening forcing certain joints of the complex to take the brunt of the punishment.
it is safe to say that you need to slow down on your volley balling, get theMRI test as your doctor has suggested, visit a good sports physio to assist you in correcting the issues that you might have with your shoulder...
If you feel you need to keep playing volleyball then you need something to help stabilize or at least show you where the stability should be when trying to smash. My suggestion is the sports physio can try some taping techniques with you..
the last suggestion would be to work with your volley ball coach to get the right technique when playing this sport to avoid future injuries...
Best of luck