Context: Social support is an important consideration during athletes’ rehabilitation following a concussion. Yet, its influence during the return-to-sport (RTS) strategy has been underexplored. Design: Concussed athletes’ experiences with social support during RTS were explored prospectively using an explanatory sequential mixed methods design. Methods: University rugby, basketball, and track and field athletes (N = 8) from a single Canadian institution, 19–23 years of age (mean = 20.63, SD = 1.51), completed concentric circles maps, the Perceived Available Support in Sport Questionnaire, and 2 semistructured interviews during their RTS. We analyzed concentric circles maps and questionnaire data descriptively and interview data using codebook thematic analysis. Results: Athletes identified 16 different social support agents. The 5 most important agents during RTS were athletic therapists, student therapists, head coaches, significant others, and teammates/friends. Significant others provided the most emotional (mean = 2.82, SD = 1.85) and esteem (mean = 2.63, SD = 1.85) support, and the athletic therapist (mean = 1.82, SD = 1.35) and head coaches (mean = 0.93, SD = 1.19) provided the most informational and tangible support. We generated 4 themes from athletes’ interviews: social support behaviors, contextual factors, concussion and RTS factors, and psychological readiness factors. Conclusions: The number of social support agents present, frequency of support types, and demonstration of support behaviors decreased across the concussion RTS strategy. Contextual (ie, toughness), concussion (ie, visibility), and RTS (ie, prognosis uncertainty) factors influenced athletes’ perceptions of social support agents’ support behaviors. Results add to our limited understanding of athletes’ social support during RTS following a concussion and suggest exploring the integration of behavior-specific (eg, checking in, providing reassurance, and demonstrating compassion) social support strategies to promote concussion rehabilitation and readiness to RTS.