The Portuguese side pushed the Reds all the way in a five-goal thriller at Old Trafford, and the boss is expecting another stern test in chasing a fourth straight Group H victory.
"It’s an important game in terms of if we win, we’re through to the next stage," Sir Alex told his pre-match press conference. "I think that’s the important part of tomorrow. Obviously I hope I can pick the team that'll do that.
"I know Braga’s record in Europe is good, particularly at home they can be a big threat. I think it will be a hard game but hopefully we can manage it."
While this season pits the Reds against Braga for the first time, previous experience of facing Portuguese sides has Sir Alex on his guard ahead of Wednesday's clash at the Estadio Axa.
"I respect Portuguese football," he said. "I've had many experiences of winning and losing against them. If you look at the record of Porto and Benfica in European football, it’s outstanding so I have a great respect for them.
"They still produce fantastic footballers and they're still the best at getting Brazilian players into their country and they all seem to make a big impact. It's an absolutely terrific country for producing good footballers and good teams."