A lubricant-infused surface (LIS) has been widely studied due to its potential in various industrial fields. However, the outermost lubricant layer of LIS is highly vulnerable to external shear force, which gradually degrades the slippery property. In this study, the shear flow-induced depletion of lubricant impregnated in a single cavity was experimentally investigated. The lubricant-filled three-dimensional cavity was exposed to a laminar channel flow. Temporal variations in the interfacial menisci inside the cavity were directly observed. The result showed that the depletion rate of lubricant is gradually decreased and eventually reaches a quasi-steady state after a long lapse of time. A large-scale vortex is formed near the lubricant meniscus and largely weakens the shear stress exerted on the meniscus. The formation of a large-scale vortex dramatically slows down the depletion rate of the impregnated lubricant. In addition, the effect of cavity geometry on the depletion of the lubricant impregnated in a biomimetic LIS was examined. The results revealed that a cavity with a smaller opening ratio (r/R) has better sustainability and less lubricant depletion. The present results would provide valuable insight into the design of a robust LIS system for effective and sustainable drag reduction and other applications.