The Serbian defender missed half of last season after sustaining the injury against Basel in the Champions League in December.
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“I don't think he was ever 100%, I noticed a couple of times in training that he was limping a little bit - then he started feeling tightness in his knee,” Ferguson told reporters.
“He wanted to carry on and in that situation that is what tough guys can do.
“Obviously the main operation was to correct the cruciate but when you do cruciates there is always the danger that the cartilage or meniscus is damaged also and that was the case.”