Holland international Janmaat picked up a groin injury just 18 minutes into the opening game of the Premier League season against Liverpool on August 12 and he has been on the sidelines since.
Centre-back Kaboul, who joined last year from Sunderland, played the entire match against the Reds but he has been out of action since the 3-3 draw after being struck down with a muscular problem.
However, Silva has been provided a big boost ahead of Saturday's trip to Southampton, revealing the defensive pair could be involved, although the game is likely to come too soon for Argentine Roberto Pereyra, who also has a groin issue.
"Kaboul, Janmatt and Pereyra have started to work with the team," he said. "I believe the first two will be ready for the match. We will assess the situation with Pereyra after he trains tomorrow and then make a decision."
The Hornets have started the campaign in good fashion, drawing twice against Liverpool and Brighton whilst a 2-0 victory at Bournemouth was wedged in between.