Jose Mourinho's side travel to Turin in midweek to take on the Serie A champions having fallen to a 1-0 defeat in the reverse fixture a fortnight ago.
However, the 'Old Lady' could be without a number of their stars for the clash after Allegri revealed the extent of his side's injury problems.
"Douglas Costa had a muscle problem, (Miralem) Pjanic was starting to feel a bit tired and (Blaise) Matuidi sustained a knock," he said following the 3-1 victory over Cagliari on Saturday.
"(Giorgio) Chiellini will be available on Wednesday and (Federico) Bernardeschi should be too. As for (Mario) Mandzukic, we need to take a look at his ankle and assess him."
Paolo Dybala's first-minute strike got Juve off to the perfect start at the Allianz Stadium as Juve restored their six-point lead at the top of Serie A, though Allegri insisted there was plenty of room for improvement as they look to secure a place in the Champions League knockout stages on Wednesday.
"It's not easy to win 10 out of 11 matches," he explained. "We got off to a good start but weren't able to add a second and then we disappeared from the game a little.
"We must do better defensively in our own half. We take too many things for granted. We assume we'll score two or three goals every game, but we can't always do that. We have to be capable of grinding out 1-0 wins too.
"We need to keep clear heads at all times, otherwise we can concede from the opposition's first cross and then almost concede another from Cagliari's only chance in the second half.
"It's one of the few things we're not doing so well, and we must work on it and concentrate more. Now we can focus on Manchester United.
"We must try to secure our place in the next round on Wednesday and then end this run of matches with a good result at AC Milan before the break."