Treatment options are being considered, according to the team.
Kleber, 30, who signed a three-year, $33 million contract extension this summer, is a key reserve for the Mavs and often closes games. He is averaging 6.2 points and 3.5 rebounds in 25.7 minutes per game and is considered by coaches and teammates to be one of Dallas' best defenders.
The Mavs have allowed 108.3 points per 100 possessions with Kleber on the court and 114.4 without him. The only Mavs rotation player with a better positive on/off difference in defensive rating is reserve wing Josh Green, who has missed the last three games due to a sprained right elbow.
Dallas is 1-5 in games missed by Kleber this season, including Wednesday's 105-90 home loss to the Cleveland Cavaliers.