The move is retroactive to Tuesday, when the Russian goalie possibly tweaked his groin in a 3-2 overtime loss in Toronto.
Varlamov is 0-2-1 with a 3.80 goals-against average so far this season.
He shined last season with Patrick Roy behind the bench, leading the NHL with 41 wins. That mark also broke Roy's franchise record for most victories in a single season.
Reto Berra will fill in until Varlamov returns to the net. The Avalanche play Thursday night at Ottawa and then finish up a four-game road swing Saturday in Montreal.