The Munster front rower came through a training session yesterday before the team departed and assistant coach Niall O'Donovan was confident of his inclusion at that stage. Horan came through Captain's Run session this morning and showed no adverse reaction to the injury.
Ireland coach Eddie O'Sullivan said: "Marcus is fine. He had a run-out this morning and so far everything is good. We are 95% sure he will be right for Italy.
"Obviously, something could flare up overnight, but today I'm happy with his fitness."