Domenech's side bossed possession for long periods of the game but lacked a cutting edge and were ultimately undone by a wickedly dipping free-kick by Deng Zhuoxiang in the 68th minute - his side's first shot on target.
After a 2-1 win over Costa Rica and a 1-1 draw with Tunisia, it means France will go into their World Cup Group A opener against Uruguay on June 11 in underwhelming form.
"There are always reasons to worry when you lose a match," said Domenech.
"There are days like that, that make you think you should have done better. We're always worried when we don't score a goal."
Defeat to China, ranked 84th in the world, brought France's World Cup preparations to an unhappy conclusion but Domenech sought to play down the significance of the result.
"We were against a team that did what they needed to do to frustrate us. We were lacking freshness and spontaneity," he said.
"Something was missing. I'm not saying it's not worrying, but I also say that it's only a warm-up match.
"In front of goal, spontaneity and freshness make the difference and we were lacking there. We have a week of work ahead of us."
Stunned into life by Deng's opener, France laid siege to the China goal in the latter stages and were only prevented from equalising by a combination of inspired goalkeeping from Zeng Cheng and some profligate finishing.
Sidney Govou, Thierry Henry, Andre-Pierre Gignac, Abou Diaby and Yoann Gourcuff all had late efforts saved, while centre-back William Gallas miscued when presented with an unprotected goal deep into injury time.
"If we look at the match and the number of chances - I don't know how we managed to miss the last one - we knew how to create chances," said Domenech.
"We were missing the final touch and against us there was a goalkeeper who performed miracles."
France goalkeeper Hugo Lloris, one of the team's most consistent performers in recent months, was embarrassed by Deng's winning goal, as his free-kick dipped sharply to leave the Lyon man floundering.
The Jabulani match ball designed for the World Cup has received criticism for its lightness from a number of high-profile players and coaches, and Domenech said it was likely to cause to havoc in South Africa.
"This ball is a ball for scoring goals. You just have to shoot at goal," he said.
Asked for the evening's low points, Domenech said: "That (Uruguay coach Oscar) Tabarez watches and finds them himself."
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