Charlton skipper Johnnie Jackson has been ruled out for several weeks with a hamstring injury.
The 29-year-old midfielder fell badly towards the end of the League One leaders' clash with Brentford and a scan has revealed substantial damage.
Addicks' boss Chris Powell told the club website: "It's a big loss losing our captain for a number of weeks.
"It shows the value of a big squad. One of the reasons I moved for Hogan Ephraim was to cover that area."
Jackson is one of five Charlton players to have started all 18 of the club's matches this term. The Camden-born midfielder has scored eight goals.
Club physio Erol Umut added: "The scan on Monday revealed significant damage and he'll be having treatment every day.
"The programme is designed to build it back up to full strength and we aim to get Johnnie back as soon as we can."