depends on the nature of your shoulder injury. many times, you can find alternate movements that you can substitute in. for example, i had a very bad injury to my sub-scapular muscle when i let my shoulder get internally rotated doing heavy pressdowns with the rope. result was i found myself unable to do any pressing movements because that muscle stabilizes the upper arm and to load it up with as little as 50 pounds in a bench press was excruciating.
i soon found that i couldn't military but i could do pull to chins and lateral raises. i couldn't bench but i could do a reasonalbe amount of weight in flies if i held my arms just so. you have to find a way if its possible.
in the meantime, you ought to be able to shrug, do deads, and all manner of leg movements. if gripping the bar hurts in squats, just push your hands out all the way to the plates and drape them over the bar. move slowly and stay in control and you should manage.
most important is don't just stop. you worked hard for all that muscle, don't just throw it away. do what you can. also, get that shoulder evaluated by a medical professional.