Speaking on the eve of United's opening European fixture against Galatasaray, the manager insisted that his defenders need to avoid injuries - and reiterated that "careless" mistakes must not be made - in order for the Reds to improve on last season's group stage.
"I think the key is to keep the defenders fit," said Sir Alex at Tuesday's press conference. "I mean that. We had a rough ride with defenders being injured in the last two or three years. If they remain fit that gives us a better opportunity.
"At the moment with [Chris] Smalling and [Phil] Jones out long-term, I'm down to three centre-backs - [Nemanja] Vidic, [Rio] Ferdinand and [Jonny] Evans. If I could be guaranteed two would be fit for the rest of the season, I'd gladly take that right now. But that's not been the case over the last few seasons. It's a key issue for us and we can't hide it. I just hope we get a bit of luck in that respect."
If United's defence can remain resolute, then Sir Alex is confident the Reds can maintain winning margins and not suffer the same lapses which enabled Basel and Benfica to benefit from relatively high-scoring draws at Old Trafford last term.
"Finishing off games has to be a driving force for us," admitted Sir Alex.
"I think we all agree we were careless in two of the games at home last season. The Basel game was the one where the criticism quite rightly lies. We were 2-0 up and playing well and then got careless in the second half and ended up drawing 3-3. That ended up knocking us out, really. We had to go there [to Basel] and get a result and we ended up