Albion hero Moore confirmed in a statement last night he was suffering with the infection, having only returned this week from a period of isolation with Covid-19.
The 46-year-old, who both played for and managed the Baggies, will now spend time away from Hillsborough as he looks to recover his health.
He said: “I have developed pneumonia as a result of COVID-19, with blood clots on the lungs and extreme discomfort.
“I am gutted to be away but I understand the situation and the course of action I must take.”
Moore made more than 100 appearances for Albion and was part of two promotion-winning teams.
After an extended spell coaching in the club's academy, he stepped up to manage the Baggies for a 12-month period in 2018 and 2019.
He joined Championship strugglers Wednesday from League One Doncaster at the start of last month.