This paper explores how informal learning can be assessed in the work environment which bears difficulties, as informal learning is largely invisible and people lack awareness of informal learning. We perform an exploratory case study involving 24 healthcare professionals representing small and medium sized enterprises (SME) in six healthcare networks in the UK. We use the existing revalidation procedure as implemented by the National Health Service (NHS) England to discuss our results. Our results comprise a description of six indicators, three of which can be used to assess informal learning activities and three of which can be used to assess informal learning outcomes. Our findings stress the importance of the social context of informal learning at the workplace. Finally, we discuss the implementation of these indicators to support informal social learning.