Under new Napoli manager Maurizio Sarri, Hamšík returned to playing as a central midfielder on the left in Napoli's three-man midfield for the 2015–16 season, which he described as being his preferred role. On 23 August 2015, Hamšík scored the opening goal in a 2–1 away defeat to Sassuolo on the opening match of the Serie A season. On 17 September, he scored in a 5–0 win over Club Brugge in the group stage of the Europa League. He made his 300th Serie A appearance on 6 January 2016, scoring in a 2–1 home win over Torino. In the following league match, on 10 January, he made his 300th Serie A appearance for Napoli in a 5–1 away win over Frosinone, as Napoli finished the first half of the season as unofficial "winter champions". He marked the occasion by scoring a goal, his 80th in Serie A, all of which were scored with Napoli.