"We're way off what Juan Pablo should be and we've really got to bring him up to speed because he's missed a lot of training," O'Leary told the club's official website.
"I think he's still feeling that injury and it's still at the back of his mind.
"If we've got any way of playing now against Southampton he's got to join in by tomorrow.
"If not, I think the Southampton match becomes a big doubt for him."