The two most important players in Manchester United's squad at the moment are McTominay and Eriksen. Manchester United will not be able to perform normally if these two players are not on the team due to injury. Manchester United will play against Leeds in two matches and against Barcelona in a Europa League match. If the squad is not stable, United will not be able to win. Despite playing well against Leeds, United will definitely need a full-strength squad to win against Barcelona.
Your version may be that the duo of McTominay and Eriksen are the best in Manchester United's midfield, but our version is different where Casemiro and Eriksen are much more optimal in organising the Red Devils' midfield. Casemiro as a destroyer of attacking lanwan as well as a counterweight while Eriksen as a supplier of the ball forward.
Eriksen became one of the key players at Man United this season, so when he gets injured, it seems to have an impact on Man United's performance. But I don't think McTominay was at his best and I think the ideal mid-position that Man United has so far is Eriksen and Casemiro.
Leeds United are still below Manchester United in quality as a whole, but Leeds United can also surprise because the Premier League is an unpredictable competition. But somehow what makes us believe that Manchester United will be able to beat Leeds easily even without Casemiro. Even better if Erik ten Hag and Manchester United's plan succeeds regarding Casemiro's red card.
I agree with you, and I guess they would even have an easy win against Leeds because Man United is in great form. Casemiro's absence would be a way for Marcel Sabitzer to play and be a starter.