The 28-year-old has not featured for the club since suffering a hamstring problem in January and will now be sidelined for a little longer after going under the knife to fix an issue that has plagued him for some time.
Nevertheless, the former Manchester United man is still thought to be confident of returning to action in the autumn.
"This is something I've put up with during my career so it's good to get it sorted," Cleverley told Watford's club website.
"I had been used to playing with pain in my ankle. Now that's going to be a thing of the past, I'll be fit and raring to win my place back once I've finished my rehab."
Cleverley made 23 Premier League appearances for Watford last season.
21 July 2018