Spinazzola, one of the stars of the tournament, put in another superb performance before breaking down in the 77th minute.
The Roma wing back, 28, broke down in tears on the Allianz Arena pitch having realised the magnitude of the injury he had suffered before being stretchered off.
And Spinazzola's worst fears were later confirmed having had scans on the injury at the Sant'Andrea Hospital in Rome on Saturday, where it was revealed he had suffered a 'ubcutaneous rupture of the left Achilles tendon'.
Italian Football Federation president Gabriele Gravina said: "I felt very sorry for Spinazzola, because he had been giving so much to this team.
"I wish him the best of luck for a quick return, because not only is he a great professional, but he has also shown great personal qualities."
New Roma manager Jose Mourinho told talkSPORT he has already spoken to the player, who told him his international teammates are very confident, while the players posted messages of support for him as they sang on the team bus.
The news, though, will come as a huge blow to Roberto Mancini, who saw his Italy side extend their unbeaten run to 32 matches in Munich.
The Italians raced into a 2-0 lead after 44 minutes thanks to brilliant goals from Nicolo Barella and Lorenzo Insigne.
Romelu Lukaku pulled one back for Belgium in first-half stoppage time, but that was as good as it got for Roberto Martinez's men.
Italy also set a new record for the longest European Championship winning run (15), which includes both qualifying and tournament matches.
Matt Holland, who was covering the game as co-commentator for talkSPORT, said on Spinazzola's injury blow: "It's heartbreaking because he's played so well.
"He was full of confidence, full of form. He played such a big part for Italy."
Italy face Spain in the Euro 2020 semi-finals at Wembley on Tuesday evening.
And Mourinho, though, he did not say Mancini's side are in the final given their last four opponents, he did struggle to find a weakness in the starting XI.
"That back four - [Giovanni] Di Lorenzo, [Leonardo] Bonucci, [Giorgio] Chiellini, Spinazzola are playing so well.
"Jorginho gives stability to the team," he added before mentioning Nicola Barella, Marco Verratti and Manuel Locatelli's contribution.
"There is so much talent in there," he said before pointing out that even if the strikers are not the most clinical, goals come from a variety of positions."