Hi I Was Training A Client For The First Time

Hi i was training a client for the first time today, hes 18 on the skinnier side , first real time working out. Our session went fine with no pain although he has a rough time controlling any weight, 3 days later he texted me saying he hurt his elbow and it "may" have been from us working out, he said it was a slipped ligament yet he had not gone to the doctor yet. Just wondering if it could have been a pre existing condition or something else. just to be clear there was no pain during or immediatly following. He said he didnt experience pain till hours after.