The English Institute of Sport has warned that David Beckham's travel schedule will harm his performance and increase his chances of injury.
Air travel has a negative impact on our ability to recover from injury
Ken van Someren, who is responsible for the health of Britain's elite athletes, said Beckham's frequent flying was a cause for serious concern.
"The problems are twofold: a reduced performance and an increased risk of injury," van Someren told BBC Sport.
"I would want to track very carefully how that athlete was coping."
Air travel has short-term and long-term effects on performance, van Someren explained. The short-term effects - such as sleep disturbance and dehydration - can be significant but are usually manageable. The long-term effects, more commonly known as jetlag, have a greater impact.
"The main challenge with long-haul flights that cross so many time zones is that your body clock is going to be out of sync with the local time," said van Someren, the EIS's national physiology lead.
"All of our bodies have a natural rhythm - the circadian rhythm - and as a result body temperature, muscle strength, joint flexibility and mental performance all tend to peak in the late afternoon or early evening.
"Now if you fly somewhere that is eight hours different (the time difference between Los Angeles and London) you are not going to be at your peak for a few days - you're going to be less strong, less flexible and less alert, which is going to increase the risk of injury."
The body's potential to recover from physical exertion and injury is also diminished.
One technique that Beckham could try is to remain on his "home" time and not attempt to align his body clock to local time. The fact that most England games are in the evening - the middle of the day in LA - will help him do this.
But this will only work for short visits and will become increasingly difficult if he is exposed to daylight, as will happen when he trains with England before their five vital Euro 2008 qualifiers in the coming months, and further time-zone changes.
All scientific research suggests it takes between four to eight days for the body to fully recover from a shift of eight time zones - in one nine-day spell in October, Beckham faces four key games, will cross 20 time zones and spend over a day in the air.
If it was able to be managed everybody would be doing it, and they're not
Dr Roslyn Carbon
Pure Sports Medicine
"Four games in nine days is going to be very demanding even without the travel," said van Someren.
"Adding the acute and chronic effects of flying - the fatigue, disruption and jetlag - is going to be incredibly strenuous. Coping with all those things is going to be some challenge.
"Put it this way, when it comes to next year's Olympics in Beijing, none of our athletes will be travelling across that many time zones within a week of competition."
Dr Roslyn Carbon, a former medical director at the EIS who has been to five Olympics with the British team, agreed with van Someren's concerns and said Beckham's travel commitments were likely to be unsustainable.
"Most people who look after teams who travel a lot go to a considerable trouble to ensure the toll on the athletes isn't too much," said Carbon, who is based at Pure Sports Medicine in London.
"So if you embark on a programme of incessant travel and high-level performance then it's not rocket science to say that it is unlikely to be able to be managed.
"If it was able to be managed everybody would be doing it, and they're not.
"Certainly, at the age of 32, I can't imagine this can be done and he can continue a normal lifestyle around it."