Reading defender Ibrahima Sonko has been ruled out for the rest of the season with cruciate knee ligament damage.
The Senegal centre-back suffered the injury when he fell awkwardly in the Royals' Premiership win over Sheffield United on January 20.
The club initially hoped the 26-year-old had suffered cartilage damage, which he underwent surgery to repair, but it has now emerged his cruciate ligament is also affected.
Royals manager Steve Coppell said: 'We will be missing Sonko for the rest of this season.
'He's obviously an important player for us, but the signings we've made during the transfer window will help to compensate for his absence.'
Coppell has signed defenders Michael Duberry (Stoke), Greg Halford (Colchester) and Alan Bennett (Cork) this month.
The club have also announced that defender Curtis Osano, a late substitute against Birmingham in the FA Cup last Saturday, has joined Conference side Woking on a temporary 'work experience' basis.