Louza went down with a shoulder injury early in the second half and received strapping on the sidelines, playing on for a while longer but eventually being withdrawn after 66 minutes.
Any lengthy absence for the instrumental midfielder would come as a blow, with Watford winning their last three matches to move into the top six of the Championship.
But Gracia seemed confident Louza has not done real damage, saying afterwards: “It is the shoulder but I suppose he will be ready for the next game.”
Papy Mendy did well off the bench at Carrow Road but keeping midfielders fit for now is crucial, with Pierre Dwomoh likely to leave in January and Edo Kayembe currently away at the African Cup of Nations.
A new signing in the middle of the park is being considered, with assistant to the sporting director Valon Behrami claiming last week that the Hornets will “probably” strengthen there in the January transfer window if they can find a player who genuinely improves them.
Hector Kyprianou has started all of the last four matches, with Moussa Sissoko generally used as a substitute for a handful of minutes on the right-hand side.