Increased plantar pressure on the medial side of the plantar surface of the foot in female athletes is one of the risk factors for lower extremity injuries. Functional tests single-leg squat tests (SLST), are one of the ways to assess changes in foot plantar pressure. The main disadvantage of clinical functional tests is their subjectivity. Moreover, as a rule, these tests are performed under laboratory conditions, which is expensive and time-consuming. This paper demonstrates the evaluation of lower foot behaviour in several SLST variations by the DAid Pressure Sock System (DPSS). The research was based on the cross-sectional study, where a group of healthy female athletes was requested to perform SLST exercises under the supervision of a physiotherapist, while simultaneously the feet plantar pressure was measured with the DPSS. Based on the observations of the physiotherapist, the participants were sorted in the test group and control group, depending on their ability to perform the exercises with or without increased inversion of the foot. Meanwhile, the application of the DPSS provided an estimate of the lateral-medial deviations of the centre of plantar pressure (COP) for evaluation of the feet functionality during the SLST. A clear correlation between the medial shift of the COP value, obtained from the DPSS measurement, and the physiotherapist’s decision on the quality of the SLST was observed. It was observed that the average COP value for the test group was shifted medially, while for the control group the position of COP was shifted laterally. Therefore, the application of DPSS with SLST has a potential for athlete functional testing, as well as for the development of feedback-based training aid in the training environment to help coaches and athletes to monitor the accuracy of the foot position in various squat exercises.