Hartlepool United loanee Andrew Nelson has returned to parent club Sunderland for treatment after scans showed he has damaged medial knee ligaments.
Nelson, 19, went off injured just minutes after being introduced as a substitute in Saturday's 1-1 draw with Plymouth Argyle.
He has played four games for Pools since joining in January.
"It's doubtful that he will be able to play again this season," head physio Ian Gallagher told the club website.
Manager Dave Jones said: "It's so unfortunate for Andrew and for us.
"He's come here looking to gain some senior experience, had done well in the games he's played and has slotted in well with the rest of the lads.