The striker, who scored the opening goal in the victory over Forest on the weekend, suffered a hamstring injury.
Helguson's replacement on Saturtday, Rudy Gestede, came off the bench to score twice to secure the home wins that's left the Bluebirds on the brink of the Premeir League.
Malky must decide if Joe Mason or Gestede gets the nod to start v Charlton. A game that City need just one point from to get promotion.
Source: Cardiff City Online