The 30-year-old was sent home from the Republic of Ireland camp on Thursday after damaging a hamstring in training the day before.
Duff Hamstring Scare!
A scan revealed a bleed in the hamstring which ruled Duff out of the World Cup qualifier against Bulgaria at Croke Park and Wednesday night's clash with Group 8 leaders Italy in Bari.
However, Newcastle's medical staff are hopeful that his recovery could take seven to 10 days, and that gives him an outside chance of making the game against one of his former clubs.