Dynamically substructured systems (DSS) are increasingly used by the dynamics testing community. DSS involves the physical testing of full size critical components in parallel with numerical testing of the remaining components. This has certain advantages over other testing methods [24]. However, the synchronization of the signals at the interface between the physical and numerical substructures of DSS requires a high fidelity controller. In practice, the performance of the DSS testing can be significantly degraded by input saturation of the actuators. In this paper, we use model predictive control (MPC) to cope with the saturation problem in DSS. To facilitate the MPC and observer design for DSS, a modified DSS framework based on an existing one is proposed [22]. As a case study, a quasi-motorcycle (QM) system is converted into the modified DSS framework and a traditional on-line MPC control strategy is implemented in real-time.