This study determined if a single bout of repeated-sprint running under hypoxic (RSH) conditions was associated with impaired cognitive function when compared with repeated-sprint running under normoxic (RSN) conditions. Eleven amateur team-sport athletes performed a repeated-sprint running protocol (4 sets of 4, 4-s all-out sprints; i.e., RSR₄₄₄) under both conditions (14.5% and 20.9% O₂) on a non-motorized treadmill. Changes in S_pO₂, pre-frontal cortex total haemoglobin (Δ[THb]), oxyhaemoglobin (Δ[O₂Hb]), deoxyhaemoglobin (Δ[HHb]) and cognitive function (detection task: DET; identification task: IDN; one card learning task: OCL; performed pre and 20 min post RSR₄₄₄) were examined. During RSH, S_pO₂ was lower following each set (p ≤ 0.05), while [HHb] was higher after each set (p ≤ 0.05) compared with RSN. In addition, while there was no effect of condition on DET (p = 0.20) or IDN (p = 0.14), OCL accuracy was lower after, compared with before, RSH (p=0.04), but not RSN (p = 0.52). A significant relationship was observed between Δ[HHB] and ΔOCL accuracy (r = -0.68, p = 0.01). Performance of a single bout of RSH with 14.5% O₂ resulted in impaired cognitive function in amateur team-sport athletes. Coaches should be mindful of timing of RSH prescription with regard to other training sessions that challenge speed and movement accuracy.