Self-heating ignition in lithium-ion batteries is a hazardous failure mode that can arise during storage or transport when internal heat generation exceeds heat dissipation, triggering venting and/or thermal runaway and potentially leading to fire or explosion. Although widely studied, previous research has predominantly focused on fresh batteries, leaving a knowledge gap regarding ignition risks in degraded cells across varied usage scenarios. In this study, we introduce a physics-based model that integrates coupled degradation and thermal runaway mechanisms to assess how self-heating ignition behaviour evolves as batteries degrade. The model, validated against experimental data, provides a predictive tool for assessing self-heating ignition risk in degraded batteries. Through this model, we reveal a strong correlation between specific degradation pathways and corresponding ignition hazards, with lithium plating identified as particularly high-risk. Additionally, we propose a self-heating ignition criticality map that introduces a critical boundary, distinguishing between conditions that could lead to self-heating ignition and those that are safe. Batteries after low-temperature cycling with severe lithium plating, exhibit reduced critical temperatures and shift from dissipation-limited to generation-limited self-heating ignition behaviours. In contrast, batteries cycled at high temperatures, where solid electrolyte interphase growth and electrolyte dry-out are the primary degradation mechanisms, show a slight increase in critical temperatures and retain dissipation-limited boundaries similar to those at the fresh state. These insights provide a valuable framework for enhancing the safety and reliability of aged batteries in storage and standby conditions.