A modified two-antenna method is proposed to measure the radiation efficiency of antennas in a reverberation chamber. By combining the conventional reference antenna method and the one-antenna method, and introducing a virtual antenna, the proposed method does not need a reference antenna with known efficiency and can be applied to highly lossy antennas, which could be problematic for the existing methods. Measurements are conducted to verify the effectiveness of the proposed method. The proposed method can be regarded as a generalized form of the two-antenna method and is compared to the existing reverberation chamber methods. The advantages and limitations of the proposed approach are also discussed.