Abstract: Multiball training is a widely used and important method in table tennis practice. The variations in the frequency and predictability of stroke-route switching across multiball drills may impose different levels of attentional demand on athletes. Previous research suggests a potential association between route-switching frequency in multiball tasks and attentional load; however, neurophysiological evidence remains limited. Using functional near-infrared spectroscopy (fNIRS), the study compared cortical activation patterns in professional athletes under three multiball conditions: a fixed-location task (low attentional load), a predictable route-switching task (moderate attentional load), and an unpredictable route-switching task (high attentional load). Results showed that, compared to the fixed-location and predictable route-switching conditions, the unpredictable route-switching condition elicited stronger activation in the left postcentral gyrus. Moreover, activation in the right precentral gyrus was significantly negatively correlated with ball stroke. Although no significant differences were observed in overall motor performance under the three conditions, the unpredictable route-switching task still induced stronger activation in sensorimotor-related cortices. This finding suggests that the action execution under high attentional flexibility demands involves additional sensorimotor integration and plan-updating processes. Collectively, these results indicate that unpredictable route-switching in multiball tasks may serve as a potential approach to modulating attentional flexibility load in training.