#3 Chelsea are missing some key players due to injury
Chelsea were dealt a huge blow as Ben Chilwell was forced off in the second half of their 4-0 win over Juventus in the Champions League in midweek. The Englishman has sustained an injury to his ACL and is likely to face a very lengthy spell on the sidelines.
Marcos Alonso has only just returned from injury and he will need to return to the starting lineup straightaway. N'Golo Kante also picked up an injury and will return only next week. Mateo Kovacic is another player who will be unavailable for the game against Manchester United.
Romelu Lukaku made the bench in the game against Juventus and will be raring to start against his former club. However, Timo Werner is expected to start ahead of the big Belgian tonight. Kai Havertz is a doubt for this one with a hamstring strain.
With some key players missing, Chelsea will have their work cut out against Manchester United.
#2 Chelsea wing-backs will be tested by Marcus Rashford and Jadon Sancho
With Jadon Sancho slowly hitting his stride, Manchester United are now more dynamic in attack. The youngster was arguably United's best player in their 2-0 win over Villarreal. He has whipped in some beauties from the right flank in his recent appearances and looks to be kicking into gear.
He scored a stunning goal to seal the deal for Manchester United against Villarreal in midweek. There is a feeling that this game might be too early for Marcos Alonso to feature but Tuchel will be forced to field him here. Alonso will need to be on high-alert with Sancho operating down his wing.
Reece James has been in spectacular form as well. But he will need to be a little cautious about getting caught in the attacking half given the fact that he has to contain Marcus Rashford.
Wing-backs are crucial to Chelsea's build-up and if Manchester United can win the ball on the flanks, they can take the game to the Blues here tonight.
#1 Cristiano Ronaldo's form
There is an argument that accommodating Cristiano Ronaldo into the team takes away from Manchester United's ability to win the ball back higher up the pitch. While that may be true, the Portuguese international's unmatched knack for goalscoring has proven to be vital for Manchester United this term.
He has also been in good form. Ronaldo assisted Donny van de Beek's goal in the 4-1 defeat at Watford. He scored a lovely lobbed goal in the game against Villarreal to put Manchester United ahead. Prior to the international break, he turned in a match-winning performance against Tottenham Hotspur.
Ronaldo scored a wonderful volley in that game and then turned creator for Edinson Cavani's first goal of the season. The 36-year-old will be waiting for a chance to impose himself tonight as well and he could once again prove to be the difference maker.