Fernando Amorebieta has suffered a setback in his recovery from a knee injury.
The Fulham defender hasn't featured since limping out of the draw against Blackpool at the beginning of the month.
Amorebieta was close to a return to the fold but has had a reaction to the problem and will miss Saturday's trip to Brighton, along with right-back Tim Hoogland.
Boss Kit Symons said: "They are both coming on but they are injuries that can't be rushed. The club's policy is to wait until they are fully-fit.
"Tim is progressing but is frustratingly slow. Fernando was getting close but was getting a lot of irritation, so we've had to take him back a little bit with his rehab."
Australian World Cup star Adam Taggart has taken another step closer to full fitness after recovering from a long-standing groin problem.
But Symons added: "He's missed a lot of football, so it will take quite a long time. He's only just back in training with the Under 21s at the moment but doing well."
Dan Burn misses the trip to the Amex through suspension, but Jack Grimmer is in contention after being recalled from his loan spell at Shrewsbury.