He received a 4-inch (10cm) tear to the groin when he was pierced by a 1,100 pound (500kg) bull, Navegante, in Saturday's fight in Aguascalientes.
The injury punctured one of Mr Tomas's veins and an artery and he was operated on immediately at the scene.
The 34-year-old bled so profusely that officials appealed over loudspeakers for compatible donors to come forward from the crowd, Mr Boix told the Spanish radio station Cadena Ser.
Mr Tomas - who has the relatively rare blood type A+ - was then taken to hospital where he underwent surgery for a number of hours, his manager added.
Despite the dangers of their profession, top-level bullfighters are rarely seriously injured in the ring.
