Izale McLeod has been ruled out for up to nine months after damaging knee ligaments.
The 23-year-old was on loan at Colchester United after joining from Charlton but he damaged his knee during only his second substitute appearance for the U's when playing against Plymouth in midweek.
McLeod has now returned to The Valley but the first prognosis suggests he will not play again this year.
"Izale sustained a spontaneous dislocation to his knee, which in turn led to the rupture of his anterior ligament," Addicks physio Steve Allen told the club's official website.
"He has also suffered significant damage to both of his collateral ligaments along with a torn meniscus.
"He will be in a brace for three weeks before undergoing reconstructive surgery, followed by intensive rehab to get him back to fitness."
Addicks boss Alan Pardew added: "Fate is playing us a tough hand this year, what with losing Toddy (Svetoslav Todorov) as well.
"Izale went out on loan just to get a few games but has ended up with a terrible injury, and there is nothing you can do about the situation now that it has happened.
"It has been a tough season for Izale, with not too many starts, and for this injury to come at this time is a big blow for the boy.
"But he is a strong character and I expect him to bounce back sooner rather than later."