Chelsea manager Enzo Maresca said he does not doubt his side is making progress but was frustrated after they conceded two early goals in their 4-2 loss to Manchester City on Saturday.
Erling Haaland scored goals in the 4th and 5th minutes at Ohio Stadium and went on to score a third as City swept past Chelsea in front of 70,000 fans.
Maresca called on his team to be "stronger" when they concede.
"We need to learn that when you concede one, you cannot concede one and then after two minutes another one," Maresca said.
"This is something that I just said to the players; we need to learn. When we concede one, we need to become stronger so we don't concede another one.
"In the first-half, apart from the first five minutes when we conceded two goals, the team was good. But it is a strange game because you plan the game in one way, then you concede two goals and it changes the dynamic."
As well as the defeat to City, Chelsea have drawn with Wrexham, lost to Celtic and beaten América this preseason. However, Maresca said he is more concerned with performances than results.
"We do not like to lose games but my main focus for me is to see things, different things, and to try to be ready for the official games at the beginning of the season," he said.
"I don't have any doubt in terms of the progress the team is doing at the moment. The mistake is part of the process.
"I knew City for many years, even in friendly games, they don't concede chances or possession but in the first-half I don't remember them making six or seven passes in a row. So that is a good thing."
