“What happens if tennis elbow is left untreated?”

Contracture.

Tennis elbow, also known as Elbow Tendinopathy, is mostly a clinical diagnosis based on examination and possibly a musculoskeletal ultrasound for confirmation. If left untreated, elbow tendinopathy can persist for 6 months to 2 years. Conservative treatment alone may not lead to resolution of symptoms. Modification of activity, counterforce bracing, splints, and physical therapy are some of the initial management measures. You can add anti inflammatory medication and steroid injections. If no relief, some investigational treatment might have some benefit. Topical nitroglycerin, ultrasound guided needle tenotomy to break up calcifications are two of the treatments under investigation. If symptoms persist, elbow tendinopathy warrants surgical evaluation.

It will either settle down by itself or continue to be painful.