"We cannot say we have players who know how to score goals," Blanc told reporters after the Group D match.
"We know we have the players to keep the ball but we don't have the players able to make the difference in the last 25 metres."
Blanc, who took over from Raymond Domenech after a woeful France were knocked out of the World Cup in the first round in June, acknowledged the players were at a low ebb.
"It is a difficult time, nothing is going our way and we have to fight this," he said.
"It is hard to see positive things when you lose. Even if you like your team, they have to score and they did not."
To add to his problems Blanc is expected to be without forwards Louis Saha and Loic Remy for Tuesday's qualifier in Bosnia.
"I will have to make tough choices because we lost Loic and Louis (tonight)," said Blanc. "Remy's injury seems serious, he felt violent pain in his groin.
"Louis felt sharp pain in his calf (after coming on as a second-half substitute). Both players are very doubtful."
Belarus coach Bernd Stange was delighted with his team's surprise win but also spared a thought for Blanc.
"It was a great start, an excellent start for Belarus," said Stange after Sergei Kislyak's 86th-minute goal sank Les Bleus.
"I think about Laurent Blanc and I know from my experience it is very difficult to build a national team in a matter of weeks."
Interact: Twitter * Facebook *Forums
