Les Bleus laboured to a 1-0 win against the United States on Friday evening, but strikers Kevin Gameiro and Karim Benzema failed to impress in a system with no proper playmaker, especially in the absence of the injured Samir Nasri.
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"We're not really used to this system. We tried to play together but it did not work out," Real Madrid striker Benzema said.
"We need a little bit more harmony between the four players up front."
Gameiro agreed, adding: "We must continue to work. I did not get a lot of balls in front of goal."
"When you have four forwards, it's hard to find space and there is no one to make the pass," said Blanc, who wishes to "experiment with the system again".
"That's the whole problem with a 4-4-2. You need one of the strikers to slip back to get and give the ball to the other."
"We have a significant margin of improvement," he said, adding that France could build on a 16-match unbeaten run. It's good for our self-confidence."
Midfielders Yohan Cabaye and Florent Malouda, who missed Friday's game through injury, took part in Saturday's training session and are expected to be fit to face Belgium at the Stade the France.
France's next friendly after that is against Germany in Bremen in February.
