In this paper, a composite tracking controller for single-link flexible manipulators is proposed. An Extended Kalman Filter (EKF) is utilized to observe the environmental forces (as disturbances) and a Lyapunov redesign robust control to alleviate the destructive effects of the observation errors in noisy situations. The observed forces can also be used in many applications such as tele-surgical robotics as interaction data. Utilizing this method, the necessity of additional force sensors is removed. It enhances structural miniaturization of the robots and reduces the costs. It should be noted that the singularity of jacobian matrix related to the flexible link, causes extreme difficulties in observation procedure which is dealt with in this paper. Moreover, control strategy is based on the common near to tip output to avoid the difficulties associated with non-minimum phase behavior of flexible link manipulators. Simulation results performed on a single-link flexible manipulator (with parameters of an experimental setup) are presented to illustrate the significant improvement in performance of the proposed controller as well as force-disturbance observation ability in noisy situations.