McCarthy is a target for Tottenham and Everton this summer.
But Quinn told the Irish Sun: "Roy Keane left Nottingham Forest when he got relegated and look where his career went - so you can't say it's not right and players should all stay loyal these days. It's not something new.
"Sometimes it's impossible for the clubs to keep the players.
"McCarthy could join one of the top four of five clubs in England.
"He has that ability, he could be the mainstay of this Ireland team - God knows we need one."