Kabasele has become a first-choice for the Hornets this season.
Martinez said Kabasele will start the friendly with Japan, another side who have qualified for next year's World Cup, as they look to end the year on a high following a disappointing 3-3 draw with Mexico on Friday.
Kabasele was stretchered off with 11 minutes to go of the 3-2 defeat at Everton before the international break, a game he had already scored in.
Allen was reportedly lined up to be senior physio but the move fell through and he remains at City.
He told the Bristol Post: "It is four years in December, it is a really good club and you are right about being linked. Listen, it was Watford, it was fine."