Kleber has been diagnosed with a fractured rib, Grant Afseth of DallasHoopsJournal.com reports.
The Mavericks ruled Kleber out of Sunday's game against the Warriors due to an illness, but the rib injury suggests he'll be sidelined for a longer period than initially expected. His absence shouldn't affect many fantasy squads, though, as he's averaging a mere 17.0 minutes per game across 14 appearances (two starts) this season.