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."