Sunderland striker Duncan Watmore may need a second operation on his injured knee after suffering discomfort on his return to light training.
The England Under 21 international, who was effectively ruled out for the rest of the season with anterior cruciate ligament damage in December last year, may now face a further spell on the sidelines.
He is due to see a specialist this week to discover whether or not further surgery is required.
Manager David Moyes said: 'Duncan Watmore might be needing a little bit of work done on his knee.