The former Tottenham stopper has played just twice this season after he limped off in Watford's 2-0 victory at Southampton back in September.
Kaboul had been expected to return to first-team action in December, but Silva, who was speaking ahead of his side's Premier League trip to Burnley on Saturday, confirmed it is unlikely the Frenchman will feature until the New Year.
"Younes is still unavailable to play and it is a big concern for us a team," Silva said. "He's a big player for us.
"We also have problems over really important players like [Nathaniel] Chalobah and doubts over [Miguel] Britos. It won't be fast but during December it looks impossible for Younes to play again."