Brown has stepped into the United defensive back-line, following Rio Ferdinand's eight-month suspension for failing to attend a drug test.
Ferdinand's absence has coincided with the champions conceding five goals in their last two Premiership outings and 24-year-old Brown has faced his fair share of criticism.
However, having fought his way back from a career-threatening injury, the England man is refusing to be downbeat about his own form.
''My fitness is getting better,'' Brown told Manchester United Radio. ''I could still be better, but the fitness is beginning to come now.
''The lads were playing brilliantly, but Rio is out for a while now and I've just come back into the side and we've let some goals in.
''I've not been playing top-notch, so I can understand it.
''I've had my ups and downs, so I won't let it get to me and will keep working at my game.''
The laidback United stopper has endured several long-term injuries and is experienced enough to recognise that match practice and regaining sharpness, will be crucial in improving his form.
With Euro 2004 taking place in the summer, Brown will be hoping an extended spell in United's first-team can catch the eye of England boss Sven-Goran Eriksson, particularly in light of Ferdinand's enforced absence.
