Inter announced his death in the early hours of Saturday, after a long illness, and said in a statement: "He was one of the greatest footballers in history. Not only in Inter's."
His funeral will be held at the Basilica of Sant'Ambrogio in Milan on Monday at 14:45.
Inter Milan will wear black armbands against Roma, and a minute's silence will be observed at every match in Italian football this weekend. Mazzola played 17 seasons at Inter, from 1960 to 1977, winning four Serie A titles, two European Cups and two Intercontinental Cups with Helenio Herrera's Grande Inter. He won the 1968 European Championship with Italy, and his 565 appearances for Inter brought 160 goals.
Gianfelice Facchetti, son of Giacinto Facchetti, the captain of the Grande Inter and Italy, paid tribute to him on Radio1 Rai.
"The fact that he left on the day San Siro turns 100 underlines how giants choose their own appointments with time. Sandro made that stadium live, made it vibrate, made it emotional, and all the others where he played.
"In the furrow of a father who could have overshadowed him, he was very good: he literally rolled up his sleeves, like Valentino. And he made his own way, with his own style, his own way of playing, becoming just as great as the father who came before him."
Valentino Mazzola, the Torino captain, died in the Superga air disaster in 1949, when Sandro was six. The son's own debut came in one of the most famous matches in Italian football. On 10 June 1961, Angelo Moratti sent a team of Inter youngsters to face Juventus in protest at a replay ordered after Juventus had already secured the title.
Mazzola, 18, was among them and, as he later recalled, had to ask his headmaster's permission to leave school. Juventus won 9-1, with six goals from Omar Sivori, but Mazzola scored Inter's goal from the penalty spot, his first in Serie A.
His name was also inseparable from Gianni Rivera's. The two were rivals, one at Inter and the other at Milan, and their duel became a permanent national debate: one or the other. It peaked at the 1970 World Cup, where Ferruccio Valcareggi introduced the "staffetta", with Mazzola starting and Rivera coming on at half-time. Italy beat Mexico 4-1 that way, and repeated it against West Germany, when Rivera scored the winner in the 4-3 extra-time classic. In the final against Brazil, Rivera came on only for the last six minutes.
Off the pitch, however, Rivera has always described a warm relationship.
"First of all he was an important opponent because he played for the other Milan team, and then because we had a great friendship. We always played together, but in Mexico it seems it was impossible. Why? Who knows, go figure the head. I've never been inside other people's heads."
Facchetti described the relationship as a misstep.
"The relationship was a hiccup along the way because it is part of that Italian vice of sometimes splitting when there are two champions and choosing which side to be on. There too you had to take both, try to make them coexist as much as possible."
Mazzola's connection with Inter did not end when he retired in 1977. He worked as a club executive, first under Ivanoe Fraizzoli until 1984 and again from 1995, when Massimo Moratti made him sporting director. It was in that spell that he brought Javier Zanetti to the club.
"I brought Zanetti in 1995," he said not long ago. He also recruited Piero Ausilio from Pro Sesto in 1998, and was involved in the arrival of Ronaldo from Barcelona in 1997: "He told me: 'OK, director, I'm coming to Milan.'"
Álvaro Recoba arrived in the same period.
Zanetti, now Inter's vice-president, wrote after his death: "Forever a legend. I owe you a lot."