The Bianconeri completed the deal to bring the 24-year-old to the club, but the midfielder will not leave the Azzurri until the market reopens in the summer months.
Jankulovski has been one of the stars of Napoli's Serie B promotion battle this season, making 18 appearances and grabbing two goals.
Napoli signed Jankulovski from Banik Ostrava in his native Czech Republic, and he is quickly becoming regarded as one of his country's best up-and-coming talents.
