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 (∆[THb]), oxyhaemoglobin (∆[O₂Hb]), deoxyhaemoglobin (∆[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 ∆[HHB] and ∆OCL 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.

• Repeated-sprint training in hypoxia (RSH) can temporarily impair cognitive function in team-sport athletes.

• Given that decrements in cognitive function may predispose athletes to knee injuries, coaches should be mindful of the timing of prescription of RSH relative to other training sessions during which knee injuries might occur.

• Repeated-sprint training in normoxia (RSN) did not affect cognitive function in the present study.