This work proposes a new joint link adaptation and HARQ (Hybrid Automatic Repeat Request) scheme for URLLC (Ultra-Reliable Low-Latency Communication) services. We consider the case where the transmitter knows only the average SNR (Signal-to-Noise Ratio) and not the instantaneous one. In the proposed scheme, the optimal maximum number of allowable HARQ transmissions and the optimal MCS (Modulation and Coding Scheme) level are determined for each packet to maximize the spectral efficiency. Our adopted approach exploits the channel diversity and increases the flexibility of the scheduling mechanism. Simulation results show that the proposed retransmission policy and link adaptation scheme increases the system performance in terms of spectral efficiency, while satisfying the latency and reliability constraints.