Report: McClean sent death threats
Police are investigating reports that the 23-year-old McClean received the threats on a social networking site.
McClean was the only Sunderland player to feature against Everton last weekend and not wear a jersey with a poppy to commemorate Remembrance Day, honoring those who sacrificed their lives in wars.
Speaking after Sunderland's 3-1 win over Fulham on Sunday, O'Neill says McClean has been criticized for his decision, including ''getting death threats as well now, so that doesn't help.''
McClean was subjected to abuse on Twitter this year after switching international teams from Northern Ireland to Ireland.