(BEDT-TTF) 3 [MnCr(C 2 O 4 ) 3 ] is the first ferromagnetic molecular metal, in which organic layers of BEDT-TTF alternate with infinite layers of the bimetallic oxalate complex [MnCr(C 2 O 4 ) 3 ] - . While the bimetallic layer undergoes a magnetic phase transition into a canted ferromagnetic state at 5.5K, the metallic character of the conductivity is not affected by the magnetic transition [Nature 408 (2000) 447]. We performed magnetoresistance measurements (B=<17T) at low temperatures (T=<900mK) and under hydrostatic pressures of up to 2.0GPa. Oscillations in the magnetoresistance develop under pressure that can be interpreted as Shubnikov-de Haas oscillations, if an internal magnetic field is taken into account. These measurements can thus be interpreted as a measure of the internal magnetic field in the conduction layer caused by the adjacent magnetic oxalate layers.