Abstract Numerical simulations are performed to investigate the role of tip injection in desensitizing a transonic compressor rotor to the detrimental effects of tip leakage flow. First, the effects of tip clearance size on the compressor stability and performance are investigated. Endwall injection of high-speed fluid upstream of the blade is then applied to the compressor with different tip clearance sizes. Results reveal that tip injection can effectively desensitize the compressor stability to the tip clearance size and improve the total pressure ratio, at the expense of some efficiency loss. It is further found that the larger the tip clearance size, the greater the stability enhancement and the smaller the efficiency penalty due to injection. The near-stall endwall flow structures for different tip clearance sizes, with and without injection, are also investigated in the current study. Results suggest that tip clearance size does not influence the compressor stalling mode, whereas endwall injection has the potential to change it (i.e., from “wall-stall” to “blade-stall” with the injection applied in the current study).