Before the tournament, the United forward was seen as the key to England's hopes of a first global title since 1966.
But the former Everton striker failed to fire in South Africa, returning home without a goal to his name after England suffered a record 4-1 tournament loss to arch-rivals Germany in the last 16 phase of the tournament.
That led to speculation that Rooney was still struggling with the ankle injury he suffered towards the end of last season.
But Ferguson told the Mail yesterday: "There is nothing wrong with the lad or his fitness. He's relaxing on holiday in Barbados and I expect him to come back refreshed for the new season."
Rooney remains United's key player as the side will hope to recapture the Premiership title next season from current champions, Chelsea.