Reds manager Gudjon Thordarson believes Peter Handyside will be out of action until Christmas after picking up an ankle injury in Sunday's FA Cup win at York City.
The Tykes captain had to be stretchered off midway through the first half after clashing with York striker Lee Nogan and Thordarson has confirmed that the news is not good.
"We lost our captain Peter Handyside through injury and that is a big, big blow to us," the Icelander told the official Barnsley FC website.
"He will be missed and he will be out for some weeks.
"We cannot tell at the moment just how long that will be but he will face a while out.
"Peter has twisted his ankle and it looks as though the ligament could have gone. He will go for a scan later today.
"We will know more tomorrow but if the ligament has fully gone then it will take six or eight weeks. He will be out for a long time."