Ireland's Chief Medical Officer Tony Holohan is in hospital undergoing tests.
However he told RTÉ that it is unrelated to the COVID-19 coronavirus.
The Deputy Chief Medical Offier at the Department of Health, Dr Ronan Glynn, is expected to take over until his release on Thursday.
Dr Holohan has held regular media briefings about coronavirus over the past month.
He appeared unwell during a briefing on Tuesday.
He then went to St James's Hospital in Dublin for treatment.