Numerous articles demonstrate how supply chain models have evolved, affecting their organisational configurations, goals, and natural relationships between suppliers and customers. Today’s supply chain is a multi-objective system traversed by numerous resource flows, but the behaviour of knowledge flow within the supply chain is not entirely understood. Numerous previous contributions have concentrated exclusively on relationships with clients and first-tier suppliers (FTS), with little or no attention paid to relationships with second-tier suppliers (STS). This article proposes a hybrid model for comprehending the process of knowledge diffusion within a triadic relationship between the customer, FTS, and STS. The model is based on two major approaches to these problems that have been proposed in the literature: Analytic Hierarchy Processes and Fuzzy Set Theory. We can determine how the triadic relationship can account for knowledge diffusion through the supply chain by examining a sample of 18 supply chains. More precisely, the research establishes a taxonomy that elucidates the role and behaviour of FTS throughout the supply chain. Numerous FTSs were identified and classified in four distinct areas. From the proposed taxonomy, this research suggests implications for customers and suppliers and delineates further additional research.