The 19-year-old winger did not train with his teammates on Saturday but instead worked by himself at the training ground.
"For tomorrow we have to wait, I cannot say it today," Flick told reporters on Saturday.
"We have to decide if it's better that he rests or he starts from the beginning, I'll speak with him and we'll decide that.
"Lamine is a player who likes to play football."
Flick said Lamine will travel with the team to Mestalla stadium, where Barca are looking to continue their 100 percent start to the season.
"He trained separately and everything was good, he will travel with us tomorrow," said Flick.
"He took a hit and he had some pain so we said it's better that he trains separately," added the coach.
"After the training he said everything was good so he will travel and hopefully he can play tomorrow."
Lamine impressed in the 5-2 win over Rayo Vallecano on Monday, netting his first two goals of the season.
Rivals Real Madrid slipped up in a 1-0 defeat at Real Betis on Friday, giving champions Barca the chance to establish themselves as sole league leaders.
"When you see the game yesterday, Real Madrid also played well... they had big, big chances," said Flick.
"This is football, (slipping up) can always happen. For us it's important that we focus on ourselves."
New arrival Gabriel Jesus is likely to begin on the bench with winger Raphinha staying as the starting striker after notching five goals in three games playing out of position.
"In this moment (Raphinha) is doing really great," explained Flick.
"He's the best option for us at the moment in this position."