A 62-year-old right-hand-dominant retired carpenter presents with 6 months of progressive right shoulder pain, inability to lift his arm above 90 degrees, and night pain. Clinical examination reveals a positive drop arm test and weakness on the Jobe empty can test. MRI shoulder with T2 fat-saturated sequences is obtained. The structure marked **A** in the diagram shows fluid signal traversing the entire tendon substance from articular to bursal side with 2 cm anteroposterior dimension and tendon retraction to the glenoid rim. Based on these imaging findings and clinical presentation, what is the most appropriate next step in management for this patient?