This paper describes a feasibility study of a novel force sensor that can be used to localise tissue abnormalities and provide tactile feedback to the surgeon during minimally invasive surgery. The proposed sensor makes use of an air-supported rigid ball mounted at the end of a tubular shaft to indent the tissue under investigation. Variations in tissue stiffness which cause changes in position of the ball are measured by using an optical sensing scheme. The sensor enables rapid acquisition of tactile information over large areas of soft tissue. Laboratory experiments were conducted to demonstrate the feasibility of the proposed sensor system. The outcome of the conducted experiments shows similarity to the results from a cylindrical wheel-based force sensor [1] which are shown here for comparative purposes.