The Southampton striker, who spent the latter half of the season on loan at Juventus, played in seven of Italy's 10 qualifiers and scored four goals in the process.
However, Osvaldo made only four starts during his time at Juve having joined following a training-ground incident at Southampton.
That lack of match action for the Serie A champions looks to have cost him a place in Brazil, with Prandelli opting to name Mario Balotelli, Antonio Cassano, Alessio Cerci, Mattia Destro, Ciro Immobile, Lorenzo Insigne and Giuseppe Rossi in his forward ranks.
Osvaldo said he expected a call-up, but insisted he held nothing against those given the nod by Prandelli.
"I had been part of this group for two years and always felt important for this (national team), so I was disappointed and upset at not being called up," he told Sky Sport Italia.
"It was a strange year for me, but having always been called in the past – and even starting in the last friendly against Spain in March – I hoped to be included.
"However, this takes nothing away from the forwards that were called. The statistics show they deserved it."
Osvaldo scored three times in 17 appearances for Juve.
