Donnarumma grew up in the football academy of Club Napoli in his native Castellammare di Stabia. At age 14, he was signed for €250,000 by Milan, the team for which his elder brother, Antonio, had already played. Between 2013 and 2015, he was part of the Rossoneri youth academy, where he always played in the age group above him, beginning with the Giovanissimi, then the Allievi, and finally the Primavera. Three days before his 16th birthday, in February 2015, he received his first call-up to the senior team from manager Filippo Inzaghi; though he did not feature in the league match against Cesena, his presence on the substitutes’ bench had required a special dispensation due to his age. At the beginning of the 2015–16 season, Donnarumma was promoted to the senior team by manager Siniša Mihajlović, initially as the third-choice goalkeeper behind Diego López and Christian Abbiati. During Milan’s pre-season tour of China, he made his debut in an International Champions Cup match against Real Madrid on 30 July. Replacing López in the 72nd minute, he kept a clean sheet for the remainder of the match, but was one of two Milan players to miss his penalty shootout attempt in an eventual 10–9 loss. His subsequent starting appearance against Sassuolo in the final of the TIM Trophy saw him save two penalties in the shootout to secure Milan’s victory. Donnarumma made his competitive debut in Serie A on 25 October against Sassuolo at the San Siro stadium; chosen to start ahead of López, he helped the team achieve a 2–1 victory after three matches without a win. At the age of 16 years and 242 days, he was the second youngest goalkeeper to start a match in the history of Italian football; 13 days older than Giuseppe Sacchi, who coincidentally made his Serie A debut with Milan on the very same date, 73 years earlier. López subsequently hailed him as “the future of Milan and of Italian football”. Donnarumma kept his first clean sheet three days later in a 1–0 win against Chievo. After three successive victories featuring Donnarumma in the starting line-up, Milan avoided a defeat against Atalanta as a result of an impressive display from their goalkeeper; “Donnarumma worked miracles,” commented the Gazzetta dello Sport. His performances that year earned him a place among the top 25 of Don Balón‘s ranking of the world’s best footballers under age 21. On 15 June 2017 it was initially announced that Donnarumma would not be renewing his contract with Milan, however on 11 July, after much speculation, he renewed with Milan until 2021.