We present a novel algorithm for motion planning of a deformable robot in a static environment. Given the initial and final configuration of the robot, our algorithm computes an approximate path using the probabilistic roadmap method. We use "constraint-based planning" to simulate robot deformation and make appropriate path adjustments and corrections to compute a collision-free path. Our algorithm takes into account geometric constraints like non-penetration and physical constraints like volume preservation. We highlight the performance of our planner on different scenarios of varying complexity.