Italy begin their campaign against France at Twickenham on Saturday hoping to qualify from a Pool D which also includes Ireland, Canada and Romania.
Bergamasco made his 89th and last appearance for the Azzurri in 2012 and will be watching his brother Mauro play from the sidelines.
The 32-year-old Zebre player is not bitter at missing his fourth World Cup, he told RMC radio, reported on Wednesday by La Gazzetta dello Sport.
He believes the Italians will still show "they are hugely talented players", but fears their lack of cohesion could leave them exposed to a humiliating defeat to Canada.
"To be honest, I'm not very optimistic," Bergamasco said.
"The squad is lacking serenity and belief. And I want to be clear: I'm not saying this because I've been left out of the squad."
Bergamasco said Brunel's failure to communicate has created a culture where even those who play regularly feel excluded.
"The coach doesn't have relations with the players, he doesn't speak and he doesn't communicate with them," he added.
"He has failed to create a group, both on and off the pitch. He usually only refers to four or five players and forgets the rest. And that's not enough when there are 31 (players).
"When one of these four or five players is missing, the squad loses belief and collapses."
Italy failed to impress in the last Six Nations, save for a last-gasp win over Scotland at Murrayfield.
And in recent weeks the Azzurri, following an intensive two-month training camp, have mostly flattered to deceive.
Brunel's men lost 16-12 to Scotland in Turin three weeks ago and suffered a record 48-7 defeat to the Scots in Edinburgh a week later.
Adding to Italy's woes are the injury absences of iconic captain and No. 8 Sergio Parisse, under whose guidance Italy have often punched above their weight, as well as New Zealand-born fly-half Kelly Haimona.
Bergamasco ruled out any chance of Italy causing an upset against France or Ireland. "It will be really hard, unfortunately," he said.