Before assuming the worst (tears are possible, but unlikely) some considerations.
One, your age. If you're older (40+), tears are more likely. If you're 16, a tear is only likely if you've also been overdoing other things (like weightlifting, pitching, throwing footballs and hauling hay all in the same day, 6x a week)
Two, conditioning. If tennis serving is the only exercise your shoulder/back muscles are getting, you could be imbalanced. It's common with weekend-warrior types. PT's will have you do "opposite motion" exercises, like arm lifts and lateral pulls. Think of it this way. Joints have 2 major muscle groups controling motion; back and forth. Serving is "forth". Over-exercise this, you'll quickly outpace "back" and the joint will soon hurt because of this imbalance.
Three, stroke. If you can rule 1 and 2 out, have a teaching pro watch you and look for obvious mistakes you're making in your stroke. Example: hitting a 70mph serve with just arm motion. Makes my shoulder hurt just thinking about it.