A method for manufacturing an intermediate prepreg , intended to form at least one portion of a finished part, said prepreg being made from a composite material comprising a matrix made from a thermoplastic material and reinforcing fibers embedded in the matrix , the method comprising the following consecutive steps: - providing at least one reinforcement layer and at least one matrix sheet made of thermoplastic material ; - forming a complex with said reinforcement layer and said matrix sheet ; and - placing the complex in a prepreg production tool , the production tool being heated to a temperature higher than the melting temperature of the thermoplastic material so that the thermoplastic material impregnates the fibers of the reinforcement layer(s) in order to form a prepreg ; the method comprising, in the production tool , the following consecutive steps: - heating the complex to a temperature higher than the melting temperature of the thermoplastic material without applying pressure on said complex , - heating the complex to a temperature higher than the melting temperature of the thermoplastic material while applying a production pressure higher than atmospheric pressure on the complex , the method for manufacturing being characterized in that it comprises the following consecutive steps, before placing the complex in the production tool : - placing at least the matrix sheet in a treatment tool , - heating said sheet to a temperature lower than the melting temperature of the thermoplastic material . - providing at least one reinforcement layer and at least one matrix sheet made of thermoplastic material ; - forming a complex with said reinforcement layer and said matrix sheet ; and - placing the complex in a prepreg production tool , the production tool being heated to a temperature higher than the melting temperature of the thermoplastic material so that the thermoplastic material impregnates the fibers of the reinforcement layer(s) in order to form a prepreg ; the method comprising, in the production tool , the following consecutive steps: - heating the complex to a temperature higher than the melting temperature of the thermoplastic material without applying pressure on said complex , - heating the complex to a temperature higher than the melting temperature of the thermoplastic material while applying a production pressure higher than atmospheric pressure on the complex , - heating the complex to a temperature higher than the melting temperature of the thermoplastic material without applying pressure on said complex , - heating the complex to a temperature higher than the melting temperature of the thermoplastic material while applying a production pressure higher than atmospheric pressure on the complex , the method for manufacturing being characterized in that it comprises the following consecutive steps, before placing the complex in the production tool : - placing at least the matrix sheet in a treatment tool , - heating said sheet to a temperature lower than the melting temperature of the thermoplastic material . - placing at least the matrix sheet in a treatment tool , - heating said sheet to a temperature lower than the melting temperature of the thermoplastic material . <EOS>