Sunderland defender Wes Brown has suffered a blow in his preparations for the new season after picking up a knee injury during the Black Cats' pre-season campaign.
The 32-year-old, who has had an injury-plagued career with the North East side, is believed to have suffered ligament damage in his knee during the club's tour of South Korea.
"It could be a bad one, but we really don't know at this stage," manager Martin O'Neill told the Sunderland Echo.
"We will probably only find out once we are home and it settles down, but hopefully it won't be too bad because he's an important player for us."
Brown moved to the Stadium of Light from Old Trafford last year.