O'Neill had hoped to include the 25-year-old in his squad for Saturday's clash at Stoke but Sidwell has suffered a setback in his bid to return to action.
"Steve has had a little bit of a setback - nothing major," O'Neill told the club's official website.
"We hoped he would be training this week but it looks likely to be next Monday now.
"He is feeling stiffness in both calves now. His attempts to get back are so strong, maybe he is overdoing it."




