The Bulgarian was due to fly to Italy for talks with Fiorentina on transfer deadline day, before it emerged that he might instead be destined for Turin.
Carrera said that it was a unique situation, but one from which the Bianconeri could benefit in the long term.
"It's the first time I have seen a situation like that," said Carrera. "Seeing what happened, perhaps it is better that he did not join us as we are talking about an unreliable player."
Berbatov made his debut for the Cottagers in today's 3-0 defeat to West Ham United.