Jadon Sancho has been urged by Borussia Dortmund team-mate Emre Can to "grow up" and improve his discipline after a haircut landed him in hot water this week.
Sancho was fined by the German Football League (DFL) for violating social distancing protocols after having a trim at home without wearing a face mask.
The England international called the sanction an "absolute joke" in a tweet before deleting it.
Can, who scored the winner against Hertha Berlin on Saturday, wants to see the 20-year-old show a little more maturity.
"We know that he just has to be more disciplined in some things, but he knows that himself," Can told Sky.
"He just has to be smarter and grow up with things like that. He can't afford to make such mistakes in the future.
"You have to lead Jadon the right way. He's a great boy, even off the pitch. He doesn't do it on purpose to cause a scandal.
"Maybe he trusts too many other people in some things."
Having scored his first professional hat-trick in last weekend's thrashing of Paderborn, Sancho produced a more low-key display against Hertha as Lucien Favre's side kept their slim Bundesliga title hopes alive.