United put two defeats on the bounce behind them when they beat Arsenal at the weekend, but it was all to obvious that things are not 100% at Old Trafford, even though it wasn't what you would call the first team playing.
If Marseille managed to find the net, then they only need a score draw to progress into the next round, United must win the tie following the goalless first leg in the south of France.
Ferguson knows Didier Deschamps' team possess a sharp enough attack to get through the United defence how it is at the moment and he doesn't want a repeat of last season when they crashed out to Bayern Munich.
"The first leg was a terrible game, a shocking match," he said.
"It will be a better game on Tuesday.
"Marseille will be planning on how they're going to score a goal and I think they'll try to start the game very quickly -that's a certainty - and we have to be prepared for that.
"It will be important to defend well. All the big games will be that way for us now."