Goals from Gabriel Jesus, Martin Odegaard, Bukayo Saka and Albert Sambi Lokonga clinched the Florida Cup for the Gunners.
Tuchel admitted afterwards, "Far from relaxed. I think we deserved to lose – which is fair enough – because we were simply not good enough. We were absolutely not competitive. The worrying part is the level of commitment, physically and mentally, for this match was not the same, it was far higher for Arsenal than us.
"We can argue they played with I think their strongest line-up; they've had now together several weeks and for more than one year. They've strengthened their line-up, played the same structure, and this is the line-up they'll try to start Premier League games.
"It was not our strongest lineup and this is part of an explanation but only a little part. The other part is worrying."
Asked if Chelsea will be ready for the start of the season, Tuchel continued: "I can not guarantee. I saw today a team in Arsenal who are mentally committed to an idea of playing, a level of exhaustion, a level of physical commitment that we could not match.
"Also, a level of mental commitment that we lacked because we have a lot of players who are thinking about leaving and looking at their options. We have players that have left and I think at the moment that's obvious."
He added: "My personal feeling, I don't know if I ever lost a match in pre-season 4-0. I can't remember not winning two matches in a row in pre-season. I'm a huge fan of a strong pre-season in everything: atmosphere, feeling, performance, belief.
"I am superstitious but not in a way that I say bad pre-season has to mean a bad season. That makes no sense to me. I am in it, a part of it, and need to find solutions.
"We fly home now and we have one-and-a-half days only, on Tuesday we need to present solutions, we need to present actions. Me and the coaching staff, together with the team, need to step up and find a way through this because it hurts at the moment."
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