Full-duplex (FD) multiple-input multiple-output relaying can significantly increase the spectral efficiency of cooperative systems. As known, the loop interference (LI) is a main factor affecting the performance of FD systems. The joint source/relay precoding has been considered a promising technique to reduce the influence of LI. Unfortunately, existing methods are developed as iterative, which is not desirable from the implementation point of view. In this letter, we propose a novel design to solve the problem. The proposed scheme not only gives closed-form solutions but avoids iterative operations. Simulation results show that our design can provide comparable performance to iterative schemes; meanwhile the required computational complexity is lower.