Thorne was withdrawn after 65 minutes of the Rams’ 2-1 defeat to Leeds at the iPro Stadium.
“When he came off he said he had a bit of a twinge in his calf,” said Derby head coach Paul Clement.
“I don’t know whether that is tightness or some kind of a strain.”
Fellow midfielder Jamie Hanson was also substituted in the closing stages on his return to the side following a bout of concussion.
Clement said: “My initial impression is he was fatigued because he has not trained regularly since the Middlesbrough game.
“I’m not sure if that was tiredness or an injury.”
Derby will use the international break to assess both players, with the Rams not in action again until they travel to Deepdale to face Preston on September 12.
Clement expects midfielder Craig Bryson to be back in contention for that game. The Scotland international has been out since suffering a knee injury in the opening game of the season at Bolton.