Jamie Ward is unlikely to feature for Derby before the international break after suffering a hamstring injury in the win at Nottingham Forest.
Ward limped off after 66 minutes of the Rams' 1-0 win at the City Ground on Sunday afternoon.
The 26-year-old will undergo a scan to determine the extent of the damage.
Derby travel to Middlesbrough on Wednesday night and face Brighton at Pride Park on Saturday before a two-week break for the next round of international matches.
"It's a concern for us but we'll have Jamie assessed and see what the damage is, but it is obviously a blow," Rams coach Johnny Metgod told the club's official website.
Ward is County's top scorer this season with four goals. He has also been in the Northern Ireland squad for recent matches.
First-team coach John Metgod, meanwhile, believes Derby's younger players will have benefited greatly from their victory at Forest.
A goal from Craig Bryson gave Nigel Clough's side their third successive victory over their neighbours after Dexter Blackstock had been controversially dismissed seconds into the second half.
Metgod singled out Will Hughes for special praise after the teenage midfielder, playing in his first east midlands derby, was involved in the build-up to Bryson's strike.
"I'm absolutely sure it's an absolutely vital performance," Metgod said.
"It's a vital experience for Will Hughes even for (Paul) Coutts, I dont think we had that many players who have played a derby like that.
"It's not the whole team, so in that sense, for a 17-year-old like Will Hughes to come into a game and certainly in the second half, well people will say it made it a lot easier because of the sending off, but you still have to do it."
