The 22-year-old has emerged as one of the club's key players since he broke into the senior side in December.
Having seen numerous opposition teams attempt to contain McClean's performances in recent weeks, O'Neill believes that Republic of Ireland international now requires the help of his teammates.
"James McClean is a marked man now," O'Neill told the club's official website. "What we have to try and do is to devise ways in which he can receive the ball, where he gets a little help from us.
"Back in his early stages he was an unknown quantity and he was able to take on players one versus one, but they're backing up now and we have to find ways of helping him.
"If James has two players on him, then there has to be someone free for us and we have to try and work that one and help James out."
McClean has scored five goals this season.