The influence of a weak shear flow on the micellization of diblock copolymers in selective solvents is investigated. The micelles are described as small microgel beads and the hydrodynamic fields calculated within the Brinkman approximation. The critical micellar concentration is shown to decrease in the shear flow, leading to the possibility of shear-induced micellization. It is also shown that the aggregation number of the micelles is modified by the flow : it increases for micelles with a large asymmetry but decreases for more symmetric micelles.