The 24-year-old England international is understood to have fractured a metatarsal during Saturday's 1-1 friendly draw at Carlisle.
Barton underwent scans on the injury on Saturday night and faces six or seven weeks on the sidelines, robbing manager Sam Allardyce of his £5.8million summer signing for the opening phase of the campaign.
Allardyce is determined to bring an end to the injury scourge which has plagued the Magpies in recent seasons by introducing a scientific approach to training.
However, with Michael Owen missing the game at Brunton Park with a minor thigh strain, Barton's misfortune served as a reminder that even the most meticulous of preparation can count for little.
The former Manchester City midfielder made his Magpies debut at Hartlepool on Tuesday evening and captained the side at Carlisle.
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