The club released a statement confirming his absence from Saturday’s fixture at McDiarmid Park.
St Johnstone go into the match in 11th place, one point ahead of bottom-of-the-table Dundee with eight games of the league season remaining.
With Davidson missing, club legend Steven MacLean, formerly of Rangers, Hearts and Aberdeen, will lead the team as Davidson’s assistant.
MacLean returned to the club in 2020 to be part of the backroom staff under the manager having helped the Saints win the Scottish Cup as a player.
"The football club can confirm Callum Davidson has tested positive for COVID,” the statement read.
“The manager is fine and well at home and will be back at McDiarmid Park next week.
“Steven MacLean will lead the backroom staff from the technical area on Saturday against Motherwell.”