The invention relates to a composite reinforcement (R-2) that auto-adheres, during curing, to a diene rubber matrix. Said reinforcement can be used as a reinforcing element for a pneumatic tyre and comprises: at least one reinforcing thread (20), for example a carbon steel cord; a layer (21) of a thermoplastic polymer composition, covering each thread individually or collectively as a plurality of threads, comprising a thermoplastic polymer having a positive glass transition temperature and an unsaturated, functionalised thermoplastic styrene elastomer having a negative glass transition temperature, said elastomer carrying functional groups selected from the groups epoxide, carboxyl, anhydride or acid ester. The invention also relates to a method for producing such a composite reinforcement, and to a semi-finished rubber product or item, especially a pneumatic tyre, including such a composite reinforcement.