Borussia Dortmund say Bundesliga protocols were not breached when six players, including Jadon Sancho, got their hair cut and took photos without face masks.
Sancho, 20, and his team-mates took the pictures with the hairdresser this week without any facial protection, which goes against the league's health safety guidelines.
"He should not have done it," Dortmund sports director Michael Zorc said on Thursday. "We were all young once, 18, 19, 20."
"In this current special situation it is not only the coach and the coaching staff but the entire club that has to be careful with discipline.
"We have talked to all those involved and they assured us that all hygiene guidelines regarding visitors were adhered to. Only for the photo were the masks taken off. That is something that should not have happened of course."
The Bundesliga became the first major sports league to restart on May 16 after a break of more than two months due to the COVID-19 pandemic.
Matches are played without fans and teams must adhere to strict health guidelines that regulate the process and operation of training sessions and games.
The Bundesliga, with five games left in the season, plans to finish by the end of the month.