Youngs has won 12 caps for England since making his debut last summer
Leicester scrum-half Ben Youngs has had keyhole surgery on his left knee but is expected to be fit for the final two of England's World Cup warm-up matches.
The 21-year-old should return to action in six weeks and be available for the Wales game on 13 August in Cardiff.
A Rugby Football Union statement said: "Ben will continue his rehabilitation with the England medics in consultation with their Leicester counterparts.
"A full recovery is expected as quickly and as safely as possible."
Youngs has established himself as England's first-choice scrum-half since making his first Test start last June.
Danny Care, Richard Wigglesworth and Joe Simpson are his rival scrum-halves in Martin Johnson's initial
45-man World Cup training squad.
The tournament in New Zealand begins on 9 September.