Cunningham comeback ahead of schedule
Defender Greg Cunningham may make a surprise return to Bristol City's squad to face Derby after making a speedy recovery from an ankle ligament problem.
The Irishman was expected to be ruled out until the new year, but has been back in training this week, and could earn himself a place among the substitutes.
Manager Derek McInnes will also be able to call upon striker Steven Davies, who has been declared fit to face his former club.
Davies has shrugged off the knee problem which caused him to miss Saturday's 3-2 victory at Sheffield Wednesday.
Jody Morris and Martyn Woolford are also available for selection after recovering from their respective problems, but centre-backs Louis Carey (calf) and Lewin Nyatanga (hernia) remain absent.
Midfielder Cole Skuse (fractured cheekbone) and striker Jon Stead (groin) are also ruled out.
Derby defender Jake Buxton is a definite absentee for their trip.
The 27-year-old was ruled out for up to eight weeks on Thursday after it was discovered he suffered medial ligament damage in his right knee during last weekend's win over Leeds.
Fellow defender Mark O'Brien replaced him on the day and could deputise again while Kieron Freeman provides further options at the back.
Midfielder Will Hughes is also a doubt after picking up an ankle knock against United. The youngster has not trained this week and will be assessed ahead of kick-off.
But manager Nigel Clough could be boosted by the return of Scottish midfielder Craig Bryson.
He has missed the last two games with a knee injury but returned to training earlier this week and is expected to travel after suffering no adverse reaction.
Striker Jamie Ward remains sidelined with a hamstring problem but Clough confirmed he could return before the new year.
"Jamie is coming on but is not close to playing at the moment. We would hope to get him back some time over Christmas," he told the Derby Telegraph.