Foden is expected to be on the sidelines for "a number of weeks" after damaging his ankle ligaments in action for Northampton Saints on Friday evening.
Catt said: "Losing a player like Fodes, with the x factor he brings, is a huge disappointment.
"He's exceptionally talented with the ball and a fantastic guy to work with. This is a big blow but it gives someone else an opportunity to come in and show what they've got."
Harlequins full back Mike Brown is expected to replace Foden for the match against Fiji on November 10.