The 37-year-old LA Galaxy midfielder had been widely expected to feature after his assistance in promoting the London 2012 Games but manager Stuart Pearce has instead selected Manchester City defender Micah Richards and Wales internationals Craig Bellamy and Ryan Giggs as his over-age players.
Following his omission he explained that MLS should be appreciated as a competitive league, and told The Sun: "The differences in levels are not that different.
"In the last five years we’ve seen the likes of Real Madrid, Barcelona and Manchester United coming over here to spend their pre-season playing MLS teams.
"That tells you something because you don’t get the likes of Sir Alex Ferguson or Jose Mourinho bringing their teams over if it’s not competitive.
"It’s great for fans. For the supporters to see [Wayne] Rooney and [Cirstiano] Ronaldo — those are the best in the world. The young kids see them play and to be able to play against these teams is a real honour.
“The level of play has gone up in the last five years.
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Beckham also added that he had no plans to retire just yet and that he was still very much enjoying playing and helping young players develop.
"I still feel like I have a good few years left," he said.
"Yes I’m 37 but I love waking up in the morning and look forward to training. When that changes I’ll realise it’s time to stop.
"I still enjoy being out there and playing. I still want to continue to be successful, work hard and to also help young players we have in the team become better.
"Me being on the field helps them in a way that can give them my experience that I have gained in the last 20 years."