In this paper, a new stability robustness analysis for discrete time systems with real parametric uncertainties is proposed. This analysis provides an upper bound of the stability hypersphere radius but also the parametric worst-case i.e. the direction in parametric space which drives straightforwardly the system to instability. This method is based on duality between the quality of the fictitious closed-loop identification of uncertain parameters and the closed-loop stability robustness w.r.t to these parameters.