The former Derry City winger has voluntarily come off Twitter and the Black Cats' boss insists that the player has not been fined for his behaviour
The 23-year-old winger was subject to criticism from Gregory Campbell, a Democratic Unionist Party (DUP) Member of Parliament (MP) after expressing his enjoyment of the Irish folk band The Wolfe Tones, on Twitter.
Reports emerged that McClean had subsequently been forced off the social networking site and fined by the club, with suggestions that there were issues with the player's attitude both on and off the pitch.
However, O'Neill has quashed the reports, stressing that the player was training well, and insisted that McClean had not been fined by the club.
"I'll deal with things internally, but he hasn't been fined," O’Neill told the Evening Chronicle. "James has voluntarily come off Twitter and I think he now feels that concentrating totally on football issues is the most important thing for him."
He continued: "Sometimes when you are tweeting you might feel as if you're speaking to three or four friends, but this is for public consumption.
"I think he realises the best thing is to leave things alone and concentrate on footballing issues. That's very important in a game which can be excellent for you, but if you take your eye off the ball, you can disappear very, very quickly," added the Black Cats' boss.
Sunderland host Fulham at the Stadium of Light in the English Premier League on Saturday, February 2.