Upton was in the England starting XI for the eighth time in the last 14 internationals as they lost 1-0 to Brazil in Doha on Saturday.
Related ArticlesKieran Gibbs shines for England U21sDavid James's World Cup place in doubtSilva: England gave ball away quite easilyEngland prepared to fail against BrazilJohn Terry: Brazil nothing to worry aboutHe said: "Losing at West Ham is not affecting my performance. You take pride in that no matter where the team is.
"It is not easy and it probably is better to be somewhere where you are winning matches, but West Ham is where I am at. I have a job to do for them.
"I don't think I have made that many mistakes individually this season but we have conceded a lot of goals. That is a problem and something we need to get better at.
"I won't let that affect my international aspirations. I am at West Ham. That is my club."
As regards his future, Upson said: "If something is put in front of me, and I have to make a decision about my future, then I will.
"At the moment it is not something I am thinking about. I am a West Ham player. Unless something happens, I am fully concentrated on them."
Upson is confident England can compete successfully against Brazil if they can adapt to the different challenges they possess compared to facing Premier League players.
He said: "It was a difficult game. They slowed it down when it suited them. It was a fantastic game. It is great to pit ourselves against the best side in the world.
"We were missing a lot of players but that just gives others an opportunity. With the right game plan in the right situation, we can do well against them. We need to bear that in mind when we go into the World Cup."