The HV-CMOS (High Voltage - Complementary Metal-Oxide Semiconductor) pixel technology has recently risen interest for the upgrade of the pixel detector of the ATLAS experiment towards the High Luminosity phase of the Large Hadron Collider (LHC) . HV-CMOS sensors can be employed in the pixel outer layers (R >15 cm), where the radiation hardness requirements are less stringent, as they could instrument large areas at a relatively low cost. In addition, smaller pixel granularity can be achieved by exploiting sub-pixel encoding technology. Therefore, the largest impact on physics performance, tracking and flavour tagging, could be reached if exploited in the innermost layer (in place of the current IBL) or in the next-to-innermost layer. This proceeding will present studies on tracking and flavour-tagging performance in presence of HV-CMOS sensors in the innermost layer of the ATLAS detector.