Middleton's brother-in-law Prince Harry presented trophies at the race earlier this month and joked that the Duke and Duchess of Cambridge would be taking part next year.
Middleton has now responded to the quip during a reception, People reports.
"I think William's going to have to do something to get him back," she joked.
Middleton also suggested that her sister Pippa would be a better entrant in the race, saying: "I'm more of a short distance runner. My sister's more of a longer-distance runner."
The Duke and the Duchess of Cambridge attended the premiere of the film African Cats in London earlier this week.