I know injuries suck and it can be difficult watching your development/strength gains decrease. When you say trainers, do you mean athletic trainers (ATC)? If so, I would consider following their recommendation. Is it worth aggravating the injury site and having to deal with a lifelong problem? Or is it better to bite the bullet and make sure you are completely healthy so you can lift the rest of your life? You will be able to quickly regain what you lost during your recovery when the time comes.
What I would do is try to maintain as much as a range of motion as possible. Can you do upperbody movements without any additional weight, and not have pain? If so, continue doing this so that way when you start lifting regularly again you won't have to deal with flexibility problems on top of getting your strength back.
Good luck man.