The Penguins visit the Boston Bruins on Thursday (7 p.m. ET; NESN, ROOT, TVA Sports, NHL.TV), their final game before the break. The All-Star Game will be held at Staples Center in Los Angeles on Sunday (3:30 p.m. ET, NBC, CBC, SN, TVA Sports, NHL.TV).
Malkin has 22 goals and is tied with Sidney Crosby for the Penguins lead with 54 points. That was second in the NHL, two points behind Connor McDavid of the Edmonton Oilers.
Though Sullivan didn't say when the injury occurred, Malkin absorbed a hit in the corner from St. Louis Blues defenseman Joel Edmundson during a 3-0 loss at PPG Paints Arena on Tuesday. Malkin was wincing in pain and couldn't put any weight on his left leg but did finish the game.
Sullivan said Malkin will be re-evaluated after the All-Star break.
"We'll probably have more information at that point," Sullivan said.
The Penguins also announced that forward Patric Hornqvist is day to day with a lower-body injury.
