United take on Romanian champions Cluj in the Champions League smarting from their first home defeat to Tottenham for 23 years, yet knowing if they can return to England with maximum points, they will have one foot into the knock-out stages.
"The Champions League is completely different to the Premier League," said Wayne Rooney.
"If you are not at your best you get punished, which is what happened to us last season.
"We have to make sure that won't happen again this year so this is a big game for us.
"Hopefully we will get a win which will put us in a good position to go through so early on in the group."