Derby forward Kris Commons is set for at least a month on the sidelines after receiving the results of a scan on his injured hamstring.
Commons was replaced early on during the 1-0 defeat to Swansea last weekend and the scan has revealed a nine centimetre tear in his hamstring.
Manager Nigel Clough told the club's official website: "The scan has confirmed what we feared and it does mean we will be without Kris for at least a month.
"It is undoubtedly a blow because he has been excellent in recent weeks.
"He will need to show the same determination and commitment to come back from this latest setback."