Coastal and estuarine environments are characterised by acute changes in temperature and salinity. Organisms living within these environments are adapted to withstand such changes, yet near-future ocean acidification (OA) may challenge their physiological capacity to respond. We tested the impact of CO₂-induced OA on the acute thermal and salinity tolerance, energy metabolism and acid-base regulation capacity of the oyster Saccostrea glomerata. Adult S. glomerata were acclimated to three CO₂ levels (ambient 380 μatm, moderate 856 μatm, high 1500 μatm) for 5 weeks (24 °C, salinity 34.6) before being exposed to a series of acute temperature (15–33 °C) and salinity (34.2–20) treatments. Oysters acclimated to elevated CO₂ showed a significant metabolic depression and extracellular acidosis with acute exposure to elevated temperature and reduced salinity, especially at the highest CO₂ of 1500 μatm. Our results suggest that the acute thermal and salinity tolerance of S. glomerata and thus its distribution will reduce as OA continues to worsen.