Benji Kimpioka will undergo surgery on his hamstring next week and is expected to be sidelined for between three and four months.
The striker limped out of Sunderland U23s win at Aston Villa last Friday and was sent for a scan on the injury on Monday.
And it was bad news for the 20-year-old, with a specialist deciding Kimpioka needs an operation.
"Benji is going to have an operation next week on his hamstring," Phil Parkinson confirmed this afternoon.
"The specialist feels that he needs surgery, which is a real shame for Benji because he has been playing very well and has got goals for the U23s.
"As you can imagine, he's pretty down about it but we just have to get him the best possible treatment and hopefully he will come back ready to go again in three or four months."
The timing could hardly have been worse for the Sweden U21 international, with Sunderland preparing to face Mansfield Town in the FA Cup first round on Wearside tomorrow, before heading to Fleetwood in the EFL Trophy on Tuesday night.
Kimpioka has scored four goals in as many games for the U23s and Parkinson said he would have been part of the squad for at least one of those two cup games had he not picked up the injury.
Parkinson said: "Benji would certainly have figured. That was in our minds.
"I watched the video of the Villa game - obviously I couldn't go to it - and he showed a good understanding of his role.
"Everybody has been pleased with him since he came back. He was almost having his pre-season in the U23 games and he was getting right up to speed, so it's a shame for the lad and for us because he is someone we could have utilised.
"It's a blow, but injuries are one of the pitfalls of being a footballer and you have to come through the other side of it and be mentally and physically strong."
Kimpioka is the second player to suffer a serious hamstring injury playing for the U23s this season, with summer addition Morgan Feeney also needing surgery and facing a three-month spell out of action after the centre-back was injured in September.
