The centre-back was sent off in the encounter between the two sides in Romania earlier this month, meaning he will miss the Group C game at Old Trafford, where United were thumped 6-1 by Premier League leaders Manchester City just over a week ago.
That defeat, which destroyed an 18-month unbeaten home run and was described by manager Sir Alex Ferguson as the worst in his career, has been followed by back-to-back away wins and clean sheets that have owed much to Vidic who missed the City game.
Without the Serb, who had been sidelined since August with a calf injury before returning against Galati, United's back four have looked vulnerable and in need of a commanding presence - exactly what the Romanians will be hoping for.
"We have to win on Wednesday, without doubt," the Scot said on the club website. "We're at home and I expect us to win and, if we do that, it's in our hands when we play Benfica at home.
"I expect Benfica to beat Basel [on Wednesday] as they're in a bit of disarray with [coach] Thorsten Fink going to Hamburg. We'll hopefully win our game and, when we play Benfica at home, it'll be the decider in our section."
"I don't think there will be a lot of changes," Ferguson said. "Maybe two or three but no more."
"It's always been better to finish first than second," Ferguson said. "After getting the first result against Galati and then playing them again at home, we'll hopefully go into the Benfica game with eight points. That will be an important match."
Galati's trip to Manchester is their first to England and could also prove to be coach Dorinel Munteanu's last match in charge.
