Sheffield Wednesday boss Darren Moore is suffering from pneumonia triggered by his contraction of Covid-19.
The 46-year-old returned to the Owls' Middlewood Road training ground on Monday having completed the required coronavirus isolation period.
However, the former Jamaica international felt unwell after Tuesday's defeat by Swansea and must stay away from the club to recover.
Moore said he had "blood clots on the lungs and extreme discomfort".
He added he was "gutted" to again miss out on his duties but understood the circumstances behind the absence.