Derby's on-loan striker James Wilson has returned to parent club Manchester United because of a serious knee injury.
Wilson, 20, sustained the injury during training with Derby on Monday and both clubs are waiting to learn the full extent of the damage.
"On-loan James Wilson has returned to £MUFC for assessment on a significant knee injury sustained during Derby County training on Monday," United said on Twitter.
Wilson joined Derby on a season-long loan in August and has made four appearances for the Championship club, including three starts.