My Son Has A Pea-sized Nodule On His Tendon On

My son has a pea-sized nodule on his tendon on the left side of his neck yesterday he noticed it after he lifted his son that is 6 months old weighs about 20 pounds up over his head but he was laying flat on the floor and as soon as that kind of hurt and felt up there and there was this little piece is not on the tendon or ligament it's not red it doesn't hurt and he has no infection that we can narrow down as far as sore throat or anything teeth so I'm just wondering if it's anything to be concerned with did he just pulled a muscle and it caused it to come to rupture a little I mean the tendon or should we investigate it further thank you