Mattiello, making only his second start for the Flying Donkeys, was stretchered off after just 19 minutes of the Serie A game after the collision with Belgian international Nainggolan.
Although both players were left lying on the ground in pain, television replays showed Mattiello’s leg folding almost in half after his foot got stuck under Nainggolan’s leg.
The 19-year-old, who is on loan at the Verona side from Serie A champions Juventus, was later diagnosed with a broken tibia and fibula.
Juventus sent their club doctor Fabrizio Tencone to Verona immediately to assess the injury and consult with Chievo’s medical staff before Mattiello underwent surgery just before midnight on Sunday.
Mattiello is expected to be sidelined for seven months but the player was quick to allay fears with a message on his Twitter profile on Monday morning.
“Thanks to everyone for the messages of support that have given me the strength to look forward,” said Mattiello.
Nainggolan said after the scoreless draw: “He’s only a young player and he was doing so well. We wish him all the best in his recovery.”