The Brazilian attacker was the man of the match in the eyes of many observers against Marseille but the Paris Saint-Germain coach wants him to add goals to his game
The Brazil international came close to scoring a memorable strike after running half the length of the field, accelerating past several challenges in the process, yet his shot was cleared off the line and his coach wants to see better next time.
"It would've been a goal we would've talked about for a long time," the former France boss explained to the press after the Classique at Parc des Princes.
"But he did not score, even if he played a good game. Lucas must understand that an attacker must score goals.
"He is still young but he is at a big club and he must progress quickly."
Blanc did, however, temper that criticism with praise for the former Sao Paulo attacker.
"He is a wonderful player; very hard-working and professional," he added. "He has the correct mindset."
PSG's victory carried them eight points clear over second-placed Monaco and the coach was pleased with what he deemed a "successful" evening, although he would not admit to feeling that the club's lead is decisive.
"I think our situation is better than our rivals," Blanc offered. "Some might say that having too much of a gap is distracting.
"There is no ideal solution but we have started to outdistance our competitors and we will not complain."