The Newcastle United striker is in O'Neill's Republic of Ireland squad for Friday night's World Cup qualifier against Wales in Dublin.
Murphy, however, sat out this morning's training session.
The 34-year-old – who played in Saturday's goalless draw against Birmingham City – has a calf problem.
Man in life-threatening condition after 'serious collision' involving car and pedestrian in South Shields
Pair set up cannabis farm in town centre flat
Campaigners rally against Local Plan after farmland in Cleadon earmarked for 156 homes
South Shields man jailed for terrifying physical and sexual assault on woman in her own home
Met Office announces yellow weather warning for thunderstorms across North East following heatwave
O'Neill said: "Daryl Murphy is giving himself a chance. He's not ruled out yet.
"We'll see what happens with the scan."
Meanwhile, defender Grant Hanley has been forced out of the Scotland squad with an ankle injury suffered at St Andrew's.