Fabio Jalo is expected to miss pre-season and some of the next campaign after knee surgery.
The 19-year-old forward had broken into the Barnsley starting 11 recently but came off hurt on Easter Monday.
Head coach Conor Hourihane said: "He’s going to be out for a while. It’s a complicated one and I feel for him. He would have been a big part of my plans going forward. I don't expect to see him in pre-season or the start of the season.
"I am gutted for him and he’s gutted. He put in really good performances and with the ability he’s got and the way I want to play, he suits it down to the ground. He's had another knock back but he has to show the right mentality now to hit the rehab head on and come back in a better way."
