Barcelona forward Ousmane Dembele was two hours late for a training session on Sunday, sources have told ESPN FC.
Dembele, 21, was tracked down at his home by club security staff a day after starring in the 4-0 derby win over Espanyol.
In October, sources told ESPN FC that Barca had concerns about Dembele's off-pitch behaviour.
The France forward then failed to report for a training session the following month, with coach Ernesto Valverde dropping him from the squad against Real Betis as a result.
Valverde, speaking at a news conference ahead of this week's Champions League match against Tottenham, tried to downplay Dembele's lateness, but sources said the club hope the player can address the situation quickly.
Barca also have concerns about the company Dembele keeps and feel his childhood friends could do more to ensure that he remains professional.
Urbano Ortega, who was assistant to former sporting director Robert Fernandez, said Barcelona had received reports about Dembele's off-pitch conduct when signing him from Borussia Dortmund last year.
"The people that surround Dembele don't help," Ortega told radio station COPE. "When we signed him, we already knew about his indiscipline problems."
Barca want to nurture Dembele's talent rather than cashing in on him, despite a number of Premier League clubs having been linked with a move.
He has scored and set up eight goals in his last eight appearances and was selected ahead of Philippe Coutinho against Espanyol, responding with a goal and an assist.
"Something happened [on Sunday], but we will try to resolve it internally," Valverde said when asked about Dembele. "I don't have anything else to say, really.
"We will try to help the player because he has a lot of talent and we want to help him. He is a player that gives us a lot on the pitch, but we have behaviour-based rules which are the same for everyone."
Defender Clement Lenglet said Dembele's teammates were more concerned about how he was playing.
"What matters to me is what Ousmane does on the pitch, and he's doing really well," he said. "You're talking about non-sporting matters, but when he's played he's played really well.
"I understand journalists look at other things but, for me, the most important is to watch the games and to see if he's doing well."
Last month, both Gerard Pique and Luis Suarez offered support to Dembele but called on him to be more professional.
Dembele is expected to be in the squad for Tuesday's Champions League game against Spurs, with Barca having already qualified.