Derby striker Conor Doyle faces time on the sidelines after an emergency operation to remove his appendix.
The USA U23 international was diagnosed with appendicitis during a team-break to America last week and was rushed to hospital for surgery.
Doctors will not allow him to fly back to the UK until next month and manager Nigel Clough admitted that, as yet, there is no timescale for his return to contention.
Clough told Derby's official website: "Conor was in a lot of pain and we were all shocked when we realised just how serious things had got and that he required an operation.
"It's a blow for him because he's one of the young players we have on the books that are progressing nicely below the first-team."
Doyle had been on the periphery of Clough's squad after leading the goalscoring charts for the club's U21 side with four goals in five games.