Beckham was an unused substitute in England's recent friendly win over Egypt as Fabio Capello opted to look at Theo Walcott and Shaun Wright-Phillips on the right wing instead of the veteran LA Galaxy star.
The 34-year-old joined AC Milan on loan in January in an attempt to convince Capello he could still make an impact at the highest level, but he has been left on the bench several times during his spell at the San Siro.
Beckham is England's most-capped outfield player and has played in three World Cups, but he knows even that wealth of experience may not be enough to persuade Capello to name him among the final 23-man squad.
"Am I banking on going to the World Cup? No, not at all," Beckham said, quoted in several newspapers in England on Sunday. "I am not guaranteed to go to South Africa. I have to work hard and hopefully win my place. There are a good few months left and plenty of games to play, but hopefully I can carry on playing well and get in the squad."