The Irish province have another destructive prop in Cian Healy and though O'Connor insists the two are different types, he has tipped 24-year-old McGrath to continue his rapid rise.
"He's world class you know, he's been unbelievable for us, he's been great for Ireland. He's got a great future in front of him," O'Connor told 98FM.
"He carries the ball, he scrummages first class, he's great around the field. He's a great asset to the squad.
"Jack's probably more your old-school prop. He does the graft, he does the hard yards.
"There's not many players on the field, let alone front rowers, who can do what Cian does, he's a special athlete.
"But where Jack has taken his game since I've been here is phenomenal and the more he plays for us and the more he plays test rugby he will get better and better."
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