Keith was hit in the left hand by a shot during the Hawks' 5-4 overtime victory over the Nashville Predators on Monday night.
"We're going to say day-to-day but he's out for (Thursday night's) game," Hawks coach Joel Quenneville said after Wednesday's practice in South Florida.
Quenneville added that Keith, who has six assists in 11 games this season, could play "soon."
Look for Sean O'Donnell to return to the lineup to replace Keith. O'Donnell has been a healthy scratch but should pair with Nick Leddy on the back end. Steve Montador should see increased time on the Hawks' penalty-killing unit to compensate for Keith's absence.
Corey Crawford will get the start in goal for the Hawks against the Panthers.