Juggling the Champions League with the Premier League is gonna be a real, real test for Carrick. He's benefited hugely from being able to play one game per week, and from being able to pick basically the same XI every single game. It means he never has to work on anything in training except repeating what they've done already.
The thing is with Carrick is that he hasn't gone in there and revolutionised a poor team with a radical new system, he's taken charge of an expensively assembled and talented squad that was badly underachieving and has simply played the best players in their most obvious positions. A week off means they can go gung-ho into every single match.
Once his first few ideas get figured out (every manager goes through this), once he's having to rotate and adapt, once he's having to manage fitness and conditioning on top of everything else, I only see it going one way. He'll be sacked when they slump to 12th over the Christmas period and they''ll be back at square one all over again.
It was like this when Ranieri was at Leicester during the 15-16 season. Their title win was amazing, but it came from Ranieri happening across the obvious answer to their problems, playing the same XI basically every single week, and giving them days to prepare so they could give absolutely everything.
Again, their squad was nowhere near good enough on paper to win the league so the achievement of 15-16 remains one of the best ever, but once Ranieri settled on Schmeichel (38 starts); Simpson (30) Huth (35) Morgan (38) Fuchs (30); Mahrez (36) Kante (33) Drinkwater (35) Albrighton (34); Vardy (36) Okazaki (28), he almost never changed it.
Once they were in the Champions League, the system completely collapsed.
The following season, admittedly after losing Kante, their most used XI was used far less at the same time. Schmeichel (30 starts); Simpson (34) Huth (33) Morgan (27) Fuchs (35); Mahrez (36) Ndidi (17) Drinkwater (27) Albrighton (33); Vardy (33) Okazaki (21). Only Simpson and Fuchs started more games in the 16-17 season.
United's record on 3-4 days rest this season is absolutely appalling for a team of their talent and it's not got any better with Carrick in charge. In fact, Carrick is yet to win any of the games he's managed for United on 3-4 days rest. The only win they've had on 3-4 days rest this season came under Amorim at the very start of the season.
From the start of the 25/26 season their record on 5-7 days (or more days) rest is P31 W17 D8 L6 (54% win percentage), their record on 3-4 days rest is P7 W1 D4 L2 (15% win percentage). That one win on 3-4 days rest came against Burnley, a 3-2 win at Old Trafford, after they'd been knocked out on penalties by Grimsby in the League Cup.
I just don't see this going well.