Considerable evidence suggests that during the progression of complex diseases,the deteriorations are not necessarily smooth but are abrupt,and may cause a critical transition from one state to another at a tipping point.Here,we develop a model-free method to detect early-warning signals of such critical transitions(or un-occurred diseases),even with only a small number of samples.Specifically,we theoretically derive an index based on a dynamical network biomarker(DNB)that serves as a general early-warning signal indicating an imminent sudden deterioration before the critical transition occurs.