McClean - who has hit six goals this season - is expected to be included when Republic boss Giovanni Trapattoni names his squad for Euro 2012.
O'Neill said: "Damien (Duff) has been a really good player for quite some time now and James is only starting out.
"Duff has the ability to play wide right, which he does for Fulham on a regular basis. James hasn't acquired that yet but simply because I've not played him in any other position than on the left.
"Over the course of next season I can see him being able to adapt to other positions, like wide right coming in on his left foot.
"He's settling in wide left well and is adding a few strings to his bow but to be fair to Damien Duff, he's been doing it a lot longer than James."