The Argentine, 24, has struggled to find his best form for the Ligue 1 giants, who sit second to Monaco early in the campaign.
Blanc, whose side face Toulouse on Saturday, said his team's system was not the problem, urging Pastore to believe in himself.
"If I knew (the problem), I would put it into practice," Blanc said.
"The problem is this player needs to regain the confidence, he needs a lot of confidence and at this moment, he has not enough confidence.
"We have to help him."
Blanc said it would be dangerous to set up his side solely to suit Pastore, who joined PSG in a big-money move in August 2011.
"We all love him. We are expecting good performances from him. We have tried to find the best conditions for him," Blanc said.
"But I can't put only one player in the best conditions. It's dangerous for the balance of the team.
"And I repeat, the Javier problem isn't about the system.
"Last year, during some games, he played very well in 4-4-2. He was extraordinary in a lot of games. It's not a problem of system."
Blanc talked up the importance of his side's clash against 11th-placed Toulouse, despite having important games against Benfica – in the Champions League – and Marseille to follow.
"The game against Benfica is in another competition. I think players take things into consideration," he said.
"It's another competition. In championship, in all the games, away or at home, we can earn three points.
"And if we want to accentuate the last victory away (against Valenciennes), we have to win against Toulouse, even if we have a lot of respect for Toulouse."
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