The defender, with seven international caps to his name, has played in 33 of Cagliari's 37 Serie A games this season, and the 27-year-old was confident his form had helped book his ticket to Brazil.
However, agent Renzo Contratto said Astori was left a broken man after being left out of the preliminary squad by coach Prandelli.
"Undoubtedly he was very, very disappointed," Contratto told TuttoCagliari.net.
"Davide played a decent campaign and in recent years he always maintained a consistent performance. Obviously he expected to be among the 30."
Contratto put the snub of his player down to Cagliari's lack of exposure, hinting a bigger club may be on the wish list of the former Milan-owned player.
"Cagliari are a very good side, but doesn't have an international spotlight. Astori has still accumulated a certain Serie A experience as well as quite a few Italy caps," he said.
"There is only one year left on his contract. It will be necessary to make evaluations, whether to remain at Cagliari or find another solution.
"Astori is quite rightly a player with ambitions who wants to improve. He is wanted in Italy and abroad.
"Much will depend on the ambitions of the Rossoblu, as he could stay at Cagliari, but we cannot make any concrete steps forward until the club situation is stabilised."
