But Ferguson admits he is wary of falling into the trap of discounting Bayern's two prized forwards from his thoughts.
Related ArticlesVan Gaal: we are not afraid of Manchester UnitedFerguson defends Vidic over 'terrible tackle'Rooney and Ferdinand fly to MunichBayern look to 'Rib' to fill void left by 'Rob'Robben injury a blow for BayernSport on televisionFerguson said: "I don't know whether Robben or Ribery will play, but we will prepare to face those two because they are special players in Bayern's set-up.
"We have to be ready to face the best team Bayern have and that is our approach.
"If anything changes, it is easy to adjust from playing a strong team to one that is less strong. But from our point of view, Wayne Rooney and Rio Ferdinand are both fit."
Former Chelsea winger Robben missed training on Monday after aggravating a calf problem during Saturday's 2-1 defeat against Stuttgart. And Bayern coach Louis Van Gaal appeared to criticise the Dutch winger by claiming he should not have been involved at the weekend.
Van Gaal said: "It's clear that Robben is not injured, but you know his problems. His muscles are tired and I have to be absolutely sure he is 100 per cent fit.
"I was the one who said to Arjen that it would be better if he did not play against Stuttgart, but he and the doctor said he could play.
"This is a big game and we cannot have a player who is 80 per cent fit.
"I do not want to take even the smallest risk. He has to be absolutely fit and only then will I put him in the team.
"We will clearly try everything to get him fit. We need a player like Robben against a team like Manchester United, but if he is not 100 per cent fit, he won't play."
Van Gaal, who is already without the suspended German international Bastian Schweinsteiger, is expected to name Ribery as a substitute due to concerns over the Frenchman's fitness following a lengthy lay-off with an ankle injury.
Sir Bobby Charlton is to lead a United visit on Tuesday to the village of Kirchtrudering, the site of the 1958 Munich air crash, which took the life of eight Busby Babes. Charlton himself was one of the survivors.