The 28-year-old has been one of the standout performers for Italy and was impressive again in the 2-1 quarterfinal win over Belgium as he was named star of the match -- for the third time in four matches at the tournament -- despite being forced off on 80 minutes with the injury.
Spinazzola was sprinting down the left wing alongside Belgium's Thorgan Hazard when he pulled up and immediately signalled to the bench that a change was required.
He undertook an examination at Sant'Andrea University Hospital in Rome where it was confirmed he had suffered a torn tendon in his left Achilles.
"Unfortunately, we know how it's gone, but our Azzurro dream continues and this is a great opportunity to show that nothing is impossible," Spinazzola wrote on Instagram on Saturday. "I can only tell you that I will be back soon! I am certain!"
Despite leading Italy to a first major tournament semifinal since 2012, manager Roberto Mancini said after the match he was "sad" following Spinazzola's injury.
In January 2020, he saw a move to Inter Milan fall through due to an issue with a medical.
After the victory in Munich over Belgium, the in-flight entertainment in Italy's returning flight turned out to be the Spinazzola Serenade.
The loud singing and enthusiastic cheering wasn't for either of the two players who scored, but for Spinazzola, who prevented a goal that could have tied the game.
"Ole, ole, ole, Spina! Spina!'' the Azzurri players sang to their injured teammate, some banging on the overhead lockers to keep the beat.
"It's a big loss for us,'' said Lorenzo Insigne, who scored Italy's second goal on Friday. "It's very sad to see and we're all trying to get behind him.''
Information from The Associated Press was used in this report