The procedure, known as pulsed field ablation, uses short high-voltage electrical pulses delivered via a catheter threaded through a blood vessel to neutralise the small cluster of cells causing the irregular heartbeat, rather than the heat-based methods used in older ablation techniques.
Napoli's medical staff discovered the issue after McTominay was withdrawn just after the hour mark of Sunday's 2-1 home defeat by Como — a substitution head coach Massimiliano Allegri had initially attributed only to a troublesome blister problem that had limited his training in the buildup to the match.
"After the onset of a mild benign arrhythmia, Scott McTominay will undergo corrective treatment via ablation (PFA) in the coming days," the club said in a statement, adding that the Scotland international is expected to be available again after the international break.
Napoli have pencilled in his return for the home match against Frosinone on 11 October, meaning he is set to miss a demanding run of fixtures against Inter Milan, Bologna, Fiorentina and Arsenal in the Champions League.
McTominay posted his own message on Instagram to reassure supporters.
"See you soon Napoli. I won't take long," he wrote.
The absence is a significant blow given the extent of his influence since arriving from Manchester United. McTominay scored 22 goals in Serie A across his first two seasons in Naples and was central to the club's Scudetto triumph under previous head coach Antonio Conte, form so striking that Conte himself once remarked the midfielder had gone "from underdog to the best player in Serie A."
With McTominay sidelined, Italian outlets have reported that Allegri is weighing a switch away from his usual system to accommodate a more advanced role for Kevin De Bruyne, with a 4-3-2-1 or 4-2-3-1 formation among the options under consideration to offset the loss of his energy and goal threat in midfield.
For Scotland, the timing is also unwelcome. McTominay is set to miss Sebastien Pocognoli's first four games in charge as head coach, against Slovenia home and away, North Macedonia and Switzerland in the Nations League — a meaningful absence for a new manager assembling his first squad.