Coach Dan Bylsma said Malkin suffered the injury in the team's previous game, against St. Louis.
Malkin is tied for sixth in the NHL with 49 assists and is seventh in points with 72, having appeared in 60 of the team's 71 games.
Only teammate Sidney Crosby has a better points-per-game average among NHL players than Malkin's 1.20 rate.
The Russian player missed several games this season with a left-foot injury suffered in a Dec. 14 contest, and in 2010 he was out of the lineup with a right-foot injury.
The Penguins, who host Phoenix on Tuesday, are atop the Metropolitan Division and second in the Eastern Conference in points. Pittsburgh (46-20-5) trails East-leading Boston by seven points, with a game in hand.