"I'm really grateful to the LA Galaxy and AC Milan for making this happen," he wrote on davidbeckham.com. "I want to help Milan to reach the Champions League as a club with its history should be there every season.
"One of the reasons for staying at Milan is to give me the chance to play in the 2010 World Cup. I have to do everything I can do to be involved in that.
"Everyone knows how passionate I am about playing for my country and, if it gives me a better chance, I'll do anything possible to make that happen.
"Right now, I'm delighted at how things have turned out and I'll be giving my all to both Milan and the Galaxy over the coming year."
Beckham has been struggling with an ankle injury, but is confident he can take to the field against Siena on Sunday afternoon.
"Unfortunately, I picked up an ankle injury in training on Tuesday, it's responding well to treatment though and I'm hopeful I can play a part on Sunday."