I hate to be party pooper of something nice for dogs, but they shouldn't be giving human tennis balls to dogs, they need tennis balls specifically made for dogs.
Human sport tennis balls have toxic components, quicly degrade to choking hazards, and the baize damages dogs teeth.
https://www.pawtracks.com/dogs/dogs-tennis-balls/
https://animaldentalspecialist.com/
As much as I love playing tennis, these balls should stay on the court and not in your dog’s mouth. These have an abrasive coating that is just way too rough on teeth! If your dog is only an occasional fetcher, they are probably okay. But for the obsessive ball players out there (Labs, Goldens, herding breeds), avoid tennis balls altogether and stick with a smooth surface ball.