Dean Leacock has added to Derby boss Nigel Clough's central defensive problems ahead of the visit of Middlesbrough.
The Rams romped to victory over Crystal Palace on Saturday but the 5-0 win came at a cost with the news that Leacock faces several weeks out after suffering a hamstring injury.
The 26-year-old, who had played every minute of the current campaign, limped out of the Palace game midway through the second half and has now joined fellow centre-halves Russell Anderson (groin), Jake Buxton (stomach and groin), Miles Addison (foot) and Mitch Hanson (knee) on the sidelines.
With 17-year-old Mark O'Brien the only other recognised fit central defender at the club, John Brayford could be asked to continue in the middle of the back four. Brayford moved across from right-back to partner Shaun Barker after Leacock went off against Palace, while left-sided player Dean Moxey could fill in.
Meanwhile, England Under-19 striker Ryan Noble goes straight into the squad after arriving on a month's loan from Sunderland and left-back Gareth Roberts is still struggling with a hamstring problem.
Boro boss Gordon Strachan has no fresh injury or suspension worries ahead of the game.
The Scot faces a decision over whether or not to restore summer signing Kris Boyd to the starting line-up after leaving him out of the last two games, the second of which resulted in a 3-1 defeat at Watford on Saturday.
Midfielder Kevin Thomson is back in training after recovering more quickly than expected from a fractured fibula, although the trip to Pride Park will come too soon for him.
Versatile defender Tony McMahon, who has recently made two substitute appearances, is in contention following a hamstring problem.
However, Justin Hoyte remains a doubt with a similar injury and Joe Bennett (tonsillitis), Matt Kilgallon (back), Jonathan Franks (herniated disc), Willo Flood (knee) and Rhys Williams (pelvis) remain on the sidelines.