The 3-year-old is having tests, reportedly after having convulsions for the second time in two months.
The England squad gathered Tuesday for its first training session for World Cup (search) qualifying games against Austria and Poland. Beckham is expected to join his teammates Wednesday in Manchester.
Newcastle striker Michael Owen also missed the training session at Manchester United's Carrington complex because of a leg injury that forced him out of Saturday's 0-0 tie with Portsmouth.
Owen hopes to recover in time for Saturday's game against Austria, which England has to win to overtake Poland atop qualifying Group 6.
Although England will be without the suspended Wayne Rooney for that game at Old Trafford, the Manchester United striker took part in training because he is available for the Oct. 12 game against Poland.