The 21-year-old will be sidelined for at least two months after injuring both knee ligaments and his hamstring during last week’s FA Cup defeat to Wigan.
Blackwell: ‘It’s a real shame about Matthew. He’s been doing very well and this has come at the wrong time for both him and the club.
‘He’ll be out for two months, the scans have confirmed that, but Sean Gregan came in for us against Sheffield Wednesday and I thought he had a tremendous game. He gets a lot of stick and most of it’s not warranted. I’ve a lot of time for Sean.’
It is thought teenager Simon Walton could be moved from midfield into the central defence position as cover.