To start with knowing the age of the chickens would help and the story of why he "just" started mounting them?
Are they Young or you just got him?
Do they run from him and he has to chase them to breed?
Is he being ruff with them when he breeds?
Do you watch them all day---reason for asking is how do you know he is not mounting them all(the norm) and just for info how do you know "this" one hen is the only one laying?
I have been raising chickens for over 50 years and have never felt the rooster breeding them has slowed egg production---Most all my hens squat for the rooster. But anything could be Possible---just never felt that was a problem.
Many things can slow/stop egg production---many things. Age, molt, stress, snake, broodiness, chickens eating them, egg thief's, feed, etc, to name a few.