Republic of Ireland international Jason Knight is set to be sidelined for 12 weeks with an ankle injury, as a report in the British media claims it was caused by his manager Wayne Rooney in training.
Derby confirmed the extent of the injury but omitted to say just how it occurred.
According to the Daily Telegraph Rooney and Knight went in for a '50-50' challenge during a session at the club's training camp Pennyhill Park, a luxury hotel and spa in Surrey.
Rooney had joined the training match due to a shortage of numbers, with injuries already taking their toll elsewhere in the squad.
The Derby manager said: "Jason will be out for eight to 12 weeks. He has rocked his ankle, thankfully, he doesn't need surgery but needs the time to make sure he gets his ankle strong again.
"Of course (it is a huge blow), everyone knows what Knighty brings to us, he is a fantastic player, great energy, and he will be a loss, but we have to deal with that."
The news will come as a blow to Republic of Ireland manager Stephen Kenny who is now likely to be without Knight for September's crucial World Cup qualifiers against Portugal, Azerbaijan and Serbia.