Chelsea boss Enzo Maresca knows there are plenty of improvements for his team to make after the Blues were thrashed 4-1 by Celtic.

Fresh from beating Manchester City, Celtic rounded off their tour of the United States in sensational style on Saturday.

Matt O'Riley, Kyogo Furuhashi, Luis Palma and Mikey Johnston put the Bhoys 4-0 up before Christopher Nkunku grabbed a consolation from the penalty spot.

And Maresca, whose team had 10 shots on target and also hit the woodwork twice, conceded there is work to do.

"Off the ball we need to improve things," Maresca said.

"You can see sometimes we confuse when we need to play short and when we need to play a little bit longer but that is part of the process.

"We maintained a high line but when the ball is not under pressure, you need to drop.

"We are still confusing some things on the ball and off the ball. It is normal in this moment when we are trying to do something new."

Chelsea open their Premier League campaign against champions Manchester City on August 18, though the teams first face off in a friendly on August 3.

And City themselves are enduring a difficult pre-season tour so far, having suffered a 3-2 defeat to Milan on Saturday.

Erling Haaland scored again, but Marco Nasti's 78th-minute goal proved decisive for Milan.

City's defeat follows on from a 4-3 loss to Celtic, and Pep Guardiola said: "We were better than the first game.

"It was a step forward - no injuries, minutes in our legs, another test - and now we fly to another game in a few days."

Aston Villa are another Premier League team in action in the United States, and like City and Chelsea, suffered a defeat, going down 4-1 to MLS side Columbus Crew.

On the bright side, Unai Emery was able to welcome back Emiliano Buendia, who missed last season due to injury.

"The best news is his comeback," said Emery. "We are happy with his return and we have to work now with him trying to get the best of him progressively.

"The first 30 minutes he played, really, is fantastic for us and for the team."

West Ham, meanwhile, went down 3-1 to Wolves, with Julen Lopetegui coming unstuck against his former team.