Chelsea are fourth on the table, and only climbed into the top four spot after beating Watford 4-2 during the weekend.
Former Blue Chris Sutton says the Blues, who are already nine points behind City in the Premier League, are seeing the results of a poor summer transfer window.
“Keeping up [with United and City] was the important thing,” Sutton exclusively told Starsport.
“It was big to lose Costa and Matic and they knew they had to compete on the European front as well. It was always an issue.
“It was clear to everybody that they’d struggle if key players got injured as they had certain issues in key areas.
“And that’s what’s happening now.
“Last season, they were fortunate in terms of keeping players fit. They didn’t use too many players to win the Premier League.
“They needed to be lucky again but that hasn’t happened.
“The game against Palace was a big eye opener. That was a game that everybody expected them to win but they didn’t.
“We knew their lack of spending could cost them and it looks like that will be the case.”