"We've definitely got to play better at Stamford Bridge and keep it tight at the back," admitted Brown in an interview with MUTV. "Some people thought it would be an easy game for us at home, but CSKA proved what a good side they are.
"It was very frustrating to go 3-1 down. We didn't play particularly well in the first half - they kept the ball well, scored early and generally made things hard for us. But in the second half we managed to put some pressure on them, the crowd got behind us and we were lucky to get the draw.
"Qualification was the most important thing. It would have been nice to get the win, but now we've qualified we can concentrate on the league."
The Reds will indeed now spend the next few days fine-tuning their game plan for what Brown believes will United's "toughest match of the season so far" at Stamford Bridge.
"Chelsea are playing very well at the moment," declared the defender. "They're a strong side, well organised and they're scoring a lot of goals. We're going to have to go there and play really well if we're to come away with any points."