Background and Objectives: Post-COVID-19 syndrome is commonly used to describe signs and symptoms that continue or develop after acute COVID-19 for more than 12 weeks. The study aimed to evaluate a treatment strategy in patients with adhesive capsulitis (phase 1) developed in post-COVID-19 syndrome. Materials and Methods: The method used was an interventional pilot study in which 16 vaccinated patients presenting with the clinical and ultrasound features of adhesive capsulitis (phase 1) developed during post-COVID-19 syndrome were treated with infiltrative hydrodistension therapy under ultrasound guidance associated with early rehabilitation treatment. Results: Sixteen patients with post-COVID-19 syndrome treated with ultrasound-guided infiltration and early rehabilitation treatment showed an important improvement in active joint ROM after 10 weeks, especially in shoulder elevation and abduction movements. The VAS mean score before the treatment was 6.9 ± 1.66. After 10 weeks of treatment, the VAS score was 1 ± 0.63. Conclusions: The study demonstrated that the management of adhesive capsulitis (phase 1) developed in post-COVID-19 syndrome, as conducted by physiotherapists in a primary care setting using hydrodistension and a rehabilitation protocol, represented an effective treatment strategy.