Several tools and methodologies were developed for manufacturing organizations to evaluate their sustainability performance. However, the growing number of methods and tools casts some doubt upon the applicability, efficiency, and capability of those methods by real manufacturing companies. Therefore, tools that offer a standard assessment of the sustainability performance of the organization with a systematic view are much needed. On the other hand, tools are not only expected to qualitatively assess sustainability but to be capable of recognizing the opportunities that help manufacturers have a more sustainable organization. To that point, the present study will focus on the following questions: "How can we help manufacturing organizations in terms of assessing sustainability?" and "How can we help manufacturing organizations discover opportunities to reach a better state of sustainability?". To respond to the questions, the study will use the indicator-based sustainability assessment framework that has been previously introduced by the authors and to develop a composite sustainability indicator. As a contribution to the literature, knowledge extraction and formalisation methods like Formal Concept Analysis (FCA) and Association Rule Mining (ARM) are employed in the development process of the composite Indicator. In fact, FCA and ARM helped create a novel method to select and weigh and aggregate indicators and therefore develop a composite sustainability index. Furthermore, the effectiveness of the proposed framework will be examined by a real case company.