The Arsenal defeat was Chelsea's third match of their US tour
Gabriel Jesus, Martin Odegaard, Bukayo Saka and Albert Sambi Lokonga scored in a comprehensive Gunners win.
Chelsea manager Tuchel suggested his side may not be ready for their Premier League opener at Everton on 6 August.
"I am far from relaxed," Tuchel said. "We were simply not good enough. We were simply not competitive."
The Gunners dominated the match in front of a record 63,811 fans at Orlando's Camping World Stadium.
Jesus, who joined from Manchester City in a £45m deal on 4 July, put Arsenal ahead after 15 minutes, and three further goals wrapped up a comprehensive win.
Bukayo Saka celebrates Arsenal's third goal with team-mates Marquinhos and Gabriel
Arsenal have now won all three of their matches on their US tour, scoring nine goals.
Speaking after the match, Tuchel said his side "deserved to lose".
He added: "The worrying part is that the level of commitment physically and mentally for this match was far higher for Arsenal than for us.
"They played I think what is their strongest line-up and structure that you see now for several weeks. This was the line-up they will try to start for Premier League games.
"It was surely not our strongest line-up. This is a part of an explanation but only a little part and the other part is worrying.
"I cannot guarantee we will be ready in two weeks."
The match was Chelsea's third and final appearance of their US tour. They had previously beaten Mexican side Club America 2-1 and lost on penalties to Major League Soccer side Charlotte FC.
Chelsea have made two marquee signings so far this summer in forward Raheem Sterling from Manchester City and centre-back Kalidou Koulibaly from Napoli. Striker Romelu Lukaku and defenders Antonio Rudiger and Andreas Christensen are among those to have left.
Chelsea now have new owners following the takeover by a consortium led by US businessman Todd Boehly, a deal that went through after the UK government imposed sanctions on previous owner Roman Abramovich.
"I look at the last season and parts of the game where we struggled, parts of the season where we struggled, and then we got sanctioned and players left us and some players are trying to leave us, and this is where it is," Tuchel said.
"So we had an urgent appeal for quality players, a huge amount of quality players. We got two quality players but we are not competitive like this. Unfortunately you could see it today."
He said Koulibaly, who came on with 20 minutes to go was the only positive for Chelsea.
"He was the best player," Tuchel said. "He was incredibly good I have to say."
-- Courtesy of BBC Sport