The present study aims to investigate the effectiveness of oral supplementation with a nutraceutical containing Collagen, Hyaluronic Acid, Vitamin C, and Manganese in functional outcome and pain reduction in cases of shoulder rotator cuff tendinopathy compared to a cycle of intra-articular hyaluronic acid injections. The project involves the recruitment of 50 adult individuals presenting with shoulder pain and instrumental evidence of rotator cuff tendinopathy. All participants will receive one intra-articular injection of 1 ml of triamcinolone acetonide 40 mg. After the injection, participants will be divided into two groups according to Good Clinical Practice guidelines. One group will begin taking one vial per day for 56 days of an oral supplement containing Hyaluronic Acid, Collagen, Vitamin C, and Manganese (HA-COL) (Tendogenial®, B2Pharma) starting from the day following enrollment (Group 1). The other group will undergo a cycle of 3 intra-articular injections with hyaluronic acid (HA) (Hyalotend®, Fidia) (Group 2). The hypothesis is that oral supplementation with HA-COL may have the same efficacy as intra-articular hyaluronic acid treatment in reducing pain and improving shoulder functionality. Functional assessments will be conducted by a clinician unaware of the participants' group assignment. The following assessment scales will be used: Numeric Rating Scale (NRS) for pain (from 0 to 10), evaluating 3 aspects of pain: 1) pain at rest, 2) nocturnal pain, 3) pain during movement. Shoulder Disability Questionnaire (SDQ) for functionality. Assessments will be conducted at the following time points: T0) Before the administration of corticosteroid intra-articular injection (baseline). T1) Seven days after the start of HA-COL intake for Group 1 and before the first intra-articular HA injection for Group 2 (T1, seven days from T0). T2) At mid-cycle of oral HA-COL supplementation for Group 1 (28 days of intake) and seven days after the last HA injection for Group 2 (T2, 21 days from T1). T3) Follow-up at 28 days from T2, at the end of the 56-day oral treatment cycle for Group 1, and 28 days after the last injection for Group 2 (T3, 56 days from T0).