DERBY County midfielder John Eustace will be out for six to eight weeks.
The 35-year-old underwent a cartilage operation last week having played a key role in recent victories over Birmingham City, Leeds United and Ipswich Town.
Will Hughes (ankle/thigh) and Craig Bryson (hip) have returned to training ahead of tomorrow's FA Cup fourth round tie against Chesterfield at the iPro Stadium.
Hughes limped off at half-time during the Rams' home defeat by Nottingham Forest last weekend and his composure on the ball was missed as Derby let a one-goal lead slip to lose 2-1.
Head coach Steve McClaren said: "Will is back training, as is Craig Bryson and as long as they have no reaction, they should be available."
Derby are hopeful of receiving international clearance for new signing Raul Albentosa in time for the Chesterfield game.
The 'thumbs-up' needs to arrive before midday today for the 26-year-old Spanish defender to be eligible to feature against the Spireites.
Albentosa has been training with his new team-mates this week after joining the Rams last week as a free agent
The centre-back previously played for La Liga club Eibar.
Simon Dawkins is also training again after the winger missed the Forest clash.
"He had to miss out because of personnel reasons, family reasons. That is continuing this week but he has come in for a few days and he comes back into contention," McClaren added.
Derby are still looking to replace winger Jordon Ibe, who was recalled from his loan spell by Liverpool last week but McClaren has ruled out a move for Chelsea's Christian Atsu, who is on loan at Everton.
The 23-year-old is currently with Ghana at the Africa Cup of Nations.
Rams' attacking midfielder Ivan Calero could be heading to Burton Albion on loan. The 19-year-old has been training with the Brewers.
McClaren said: "We are just giving him a change of environment. We said it might be interesting to go down for a day or two and train and see if he can develop from that.
"It is about under-21 players gaining experience. We have got Kwame Thomas and Alefe Santos out on loan at Notts County."
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