The England international initially escaped punishment from the Six Nations after being caught on camera calling his Wales counterpart a "gypsy boy", but he will now face an independent misconduct hearing after World Rugby deemed that action should have been taken.
Marler has since apologised for the comments, and O'Shea has rubbished allegations of his club captain being racist.
"He is not in any way shape or form racist. He is an edgy person, he made a mistake, and he apologised," he is quoted as saying by PA.
"Does he know that he has got a responsibility? Of course he does. Do we accept it? Of course we don't, but some of the vitriol that has been directed to him is tough for a 25-year old to take and he has to take it on the chin. I am not going to talk about political correctness, I am not going to talk about banter. He knows he shouldn't have said it. He apologised at half time, he knew it was wrong.
"I had a good sit-down with him. You couldn't get anything further from a bloke that is racist going. Joe Marler is a bloody great bloke and I made him captain here for a reason. He is actually in great form because he knows that the people who know him, know how things are and the two players involved have gone 'it's done'."
England went on to win the match 25-21 on their way to a first Grand Slam since 2003.