Pectoralis Pain

My fiance has been working out for the past 5-6 months...about 3 weeks ago, he complained of pain on the left side of his pecs directly below his clavicle on the acromion end....when I would reach under his arm to hug him from behind, and put my hand on his chest and make a pulling motion down, it would buckle him....he said it hurt very bad and felt like a burning sensation and when he pushed his chest back up as if to put it back in place, and hold it there for a minute, the pain would go away...funny thing is, he says it never hurts when he works out...he's 26, 6' 2", about 215lbs, used to smoke, quit 2 years ago, and healthy otherwise.....he works out and when he does, he does bench presses, punches the punching bag, and push ups...all things associated with the upper torso...please let me know what you think.....he is a worry wart, and I want to reassure him that this is just a muscle strain/tear...and nothing to worry about....thank you for reading and I hope you reply:)

Sincerely,

A worried fiance'