United host Chelsea on Sunday in a match that will go a long way to deciding who will be crowned Premier League champions but first they need to ensure they reach the Champions League Final by not letting Schalke 04 get back into their semi-final.
Last year United handed the advantage to eventual English champions Chelsea by losing 2-1 to their rivals at Old Trafford, just days after facing Bayern Munich in the first leg of a Champions League quarter-final they went on to lose.
Having won last week's first leg in Germany 2-0, it would be a major shock if United did not reach the May 28 European final at Wembley and Ferguson should be able to rest several players to keep them fresh.
"If you look at the experience of last year where we lost the league was after a (midweek) game against Bayern. The team were very tired against Chelsea in that next game," Ferguson told a news conference.
"That has to have a bearing on my team selection. Two massive games, both as important as the other. There will be some changes, hopefully I've a nucleus of a team that is still good enough to win the match."
United are three points clear in the Premier League and Chelsea would go top on goal difference with victory this week, making it unsurprising that fans are focusing on that match rather than the Champions League game they feel is in the bag.
"That's the sort of optimism supporters have got, we don't share that because we feel we've got a lot of work to do tomorrow," Ferguson said.
"I hope Manchester United don't regard it as a formality tomorrow. I think our work ethic will be very high."
MASSIVE GAME
Ferguson has said he will pick a strong defence with changes likely to come in the attacking positions, presenting chances for strikers Dimitar Berbatov and Michael Owen and midfielder Darren Fletcher who has missed two months with a virus.
He pointed to the fact that all four Champions League semi-finalists, including Real Madrid and Barcelona, lost domestic matches at the weekend as a reason for squad rotation.
"There are certain statistics that tell you they do take it out of you the European games, which is why Sunday's game against Chelsea is a massive game," he said.
"I have to pick the right team tomorrow in order to have the same kind of freshness in Sunday's match."
Ferguson said he expected Schalke to go on the attack, as they had no other choice, but can be comforted by United's tight defence which has let in only three goals in this year's competition.
"We seem to have better concentration levels at European games because it's not regular football," the Scot said.
"The mundane football of the Premier League is incessant tribalism almost, that you're playing either a London team... or Liverpool teams, it creates that incredible competitive edge. But as you go to Europe it's a different type of football, different ways of playing."
