Background: Greater Trochanteric Pain Syndrome (GTPS) is a frequent clinical condition characterized by acute or chronic pain in the lateral region of the hip. This condition is primarily due to degenerative gluteus minimus and medius muscle tendinopathy. In a previous ex vivo study, proliferation and migration of human tenocytes and synthesis, maturation, and secretion of Collagen I (COL-I) were improved when human gluteal tenocytes were exposed to a swine-derived type I collagen available on the market (MD-Tissue—GUNA S.p.a. Milan, Italy). The study's purpose is to evaluate the effects of injecting an MD-tissue medical device on GTPS pain, hip function, and strength. Methods: The study group was treated with ultrasound-guided injections of swine-derived collagen once a week for three consecutive weeks. Primary endpoint was pain reduction of at least 3 points on the Numeric Rating Scale (NRS) for pain at ten weeks. Secondary endpoints were: NRS average reduction at rest and palpation, modified Harris Hip Score (mHHS), abductor strength, and magnetic resonance imaging (MRI) improvement at six months. Results: Fifty-two patients were screened, 47 enrolled, 43 completed the study, and 42 were available for the final follow-up. The primary endpoint was reached in more than 60% of the patients. The secondary endpoint, increased in all the timelines with statistical significance. Neither early nor late adverse effects were found. Conclusions: Ultrasound-guided peritrochanteric injections of MD-Tissue are a safe and effective treatment for the majority of the Patients affected by Greater Trochanteric Pain Syndrome.