Manchester United fullback Joe Riley has returned from his loan at Sheffield United.
Riley joined the League One leaders on loan until the end of the season last month.
And he made his debut for the Blades in last week's 0-0 draw at Bristol Rovers.
But he has now returned to Manchester United after dislocating his shoulder in a freak accident in training.
Blades boss Chris Wilder said: "It's was a bit of a freak accident in training.
"It was something an nothing. "He stumbled and fell and dislocated his shoulder.
"It's desperate bad luck for Joe and for us.
“He played last week at Bristol Rovers and can be very pleased with his debut.
"Those scan results will see if he's back with us or that's his season done."