Packet forwarding is an essential service in a multihop cellular network (MCN), which relies on the cooperation of all participating mobile terminals (MTs). Although this service can effectively improve the energy efficiency of MTs by dividing a long radio link to several shorter hops, cooperation of MTs cannot be taken for granted as they are normally controlled by rational players who seek to maximize their own benefit by taking advantage of the service while minimizing their contribution. To ensure proper operation of the network, there should be a mechanism to encourage cooperative nodes while punishing free riders. To this end, we propose a credit scheme based on coalitional game model. We provide credit to cooperative nodes proportional to the core solution of the game, which distributes the common utility among the players in a way that everyone is satisfied. Simulation results validate that the proposed technique can successfully detect and isolate selfish nodes.