The party was announced during a two-hour extravaganza on state broadcaster RAI entitled 'Blue Dream' where the players and coach Antonio Conte were brought up on stage and interviewed one by one.
AC Milan captain Montolivo, denied a place at the World Cup in Brazil two years ago after breaking his leg in a friendly, suffered a calf injury last week. De Rossi, 32, has played only four matches for Italy during Conte's two seasons in charge but injuries to Marco Verratti and Claudio Marchisio have depleted the midfield.
"I've been in the national team for so many years but this has been the first time in which I've worried about not being part of the group," said De Rossi who has played in the last three World Cups and two European Championships.
Napoli's Brazilian-born midfielder Jorginho was among seven players included in the provisional group last week who failed to make the cut.
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The squad included two other Brazilian-born players, midfielder Thiago Motta and forward Eder.
Experienced playmaker Andrea Pirlo was not included, having also been left out of the provisional group.
"It's not easy to exclude people and it's very unpleasant to leave behind people who have really given everything for this shirt," said Conte who will leave the job after the tournament to take charge of Chelsea.
Italy have been drawn with Belgium, Sweden and Ireland in Group E at Euro 2016.
Goalkeepers: Gianluigi Buffon (Juventus), Federico Marchetti (Lazio), Salvatore Sirigu (Paris St Germain)
Defenders: Andrea Barzagli, Leonardo Bonucci, Giorgio Chiellini (all Juventus), Angelo Ogbonna (West Ham United), Federico Bernardeschi (Fiorentina), Matteo Darmian (Manchester United), Mattia De Sciglio (AC Milan)
Midfielders: Antonio Candreva (Lazio), Daniele De Rossi, Alessandro Florenzi (both AS Roma), Emanuele Giaccherini (Bologna), Thiago Motta (Paris St Germain), Marco Parolo (Lazio), Stefano Sturaro (Juventus)
Forwards: Eder (Inter Milan), Ciro Immobile (Torino), Lorenzo Insigne (Napoli), Graziano Pelle (Southampton), Simone Zaza (Juventus), Stephan El Shaarawy (AS Roma).
(Reporting by Brian Homewood; editing by Ken Ferris)
