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Cells normally combine glycolysis and oxidative phosphorylation (OXPHOS) to meet energy demands, but this balance shifts under pathological conditions. During SARS-CoV-2 infection, hypoxia, viral entry, and elevated tissue lactate alter cellular metabolism. To explore these effects, we propose a parsimonious mathematical model describing how oxygen levels, viral infiltration, and extracellular lactate jointly regulate metabolic balance through HIF-1 α protein, inside the cell, accounting for lactate's biphasic, non-monotonic influence on glycolysis. Model simulations reveal a single steady state whose position on the glycolysis-OXPHOS phase plane depends on environmental conditions, namely, oxygen concentration, infection, and extracellular lactate. We identify four metabolic regimes, determined by sufficiency of energy production and the driving process (OXPHOS or glycolysis). Decreasing the oxygen shifts cells from OXPHOS to glycolysis dominance in both infected and non-infected states, but infected cells may become energy-deficient even with sufficient oxygen due to virus-induced mitochondrial damage. Rising extracellular lactate initially promotes glycolysis but ultimately suppresses it at high levels, pushing cells into severe energy deficit with inhibited glycolysis. Simulations of reoxygenation exhibit hysteresis: cells pass through an energy-deficient zone during hypoxia onset but return through a safer trajectory when oxygen is restored; a vulnerability is higher in infected cells. Overall, the model clarifies metabolic trajectories during viral infection, suggesting that early hypoxia is particularly dangerous and that severe acidosis can further collapse energy production. Preventing or rapidly reversing hypoxia in respiratory infection may protect cells from energy failure and limit harmful lactate accumulation.