The former Manchester United player recently suffered a heart rhythm problem, which is not considered serious but required surgery.
On Tuesday morning, McTominay underwent surgery, which the club described as successful.
"McTominay will rest for two weeks before resuming training," the club wrote.
McTominay, 29, has been a key player since joining Napoli in 2024 from United, scoring 27 goals in 82 appearances. He won the league title with Napoli in his first season and was named the most valuable player in Serie A.
Napoli have previously announced that McTominay will miss Scotland's upcoming Nations League matches in September and October.
