I recently noticed upper bicep popeye muscle & my shoulder hurts by my neck what could be the problem?

Popeye muscle: The most common cause is a rupture of the long head biceps tendon, which goes to the shoulder. The biceps has two tendons near the shoulder and one can commonly rupture, causing the muscle belly to move down a bit towards the elbow. It usually functions fine and the pain resolves with time. In fact, we sometimes surgically cut the tendon if it is partially torn, leading to the same result.