Chelsea have spent more than £200million to sign Hakim Ziyech, Timo Werner, Ben Chilwell, Malang Sarr, Thiago Silva and Kai Havertz.
Match of the Day host Gary Lineker has warned that signing good players does not automatically make a team better.
Lineker insists Chelsea boss Frank Lampard will have to quickly work out his best starting XI if Chelsea are to close the gap on the top two this season.
“While I’m going for the same top two, I expect Chelsea and Manchester United to provide more of a challenge,” he wrote in his column for The Sun.
“The Blues have backed Frank Lampard in the transfer market with eye-catching signings like Kai Havertz, Timo Werner and Thiago Silva.
“Of course, bringing in new faces doesn’t automatically make you better and Frank will have to work out what his best side is.
“And I’m also not sure if they have the right goalkeeper at Stamford Bridge with Kepa Arrizabalaga and Willy Caballero to choose from.
“But they will push harder this time and at Old Trafford, I can see United continuing to make progress under Ole Gunnar Solskjaer.
“He has added another good young player in 23-year-old Donny van de Beek and are looking to sign Jadon Sancho. So I think there are exciting times ahead again for them and I expect United to finish in the top four again.”