The Republic of Ireland international has spent the first half of the season on loan at Elland Road, where he began his career as a trainee.
The 25-year-old has already expressed a desire to extend his stay Yorkshire and could get his wish.
"If Leeds or someone else want to sign him then yes, I'd be prepared to sell him," said McCarthy. "He knows that. There's no secret at all. It would be good for him because he's another one who helped us get promoted.
"He's not really featured in the Premier League so it makes sense for him to move on because he needs to be playing.
"He's in their team, he's playing for a great club, he's getting regular football and he started his career there. I'm not a rocket scientist but I kind of thought he wouldn't mind staying there."