We envision deepfake technologies, which synthesize realistic fake images and videos, will play an important role in the future metaverse. While enhancing users' immersion and experience with synthesized virtual characters and scenes, deepfake can cause serious consequences if used for fraud, impersonation, and dissemination of fake information. In this paper, we introduce the principles, applications, and risks of deepfake technology, and propose some countermeasures to help users and developers in the metaverse deal with the challenges brought by deepfake technologies. Further, we provide an outlook on the future development of deepfake in the metaverse.