South Africa prop Tendai Mtawarira was treated in hospital on Saturday after suffering mild heart palpitations.
A statement on the Spingboks' official website said: "The decision to withdraw Mtawarira (from the Ireland game) is a precautionary measure after he had a recurrence of mild heart palpitations on Saturday morning.
"Mtawarira has been admitted to hospital for observation on Saturday morning. A decision on his continued participation on the tour will be taken at a later stage."
A further update said the 27-year-old was later discharged from hospital.