Borussia Dortmund boss Edin Terzic disclosed that players were only informed of Sebastien Haller's tumour after their loss to Valencia.
Dortmund played their first foreign opponent in preparations for the upcoming season on Monday, with a Goncalo Guedes brace helping Valencia to a 3-1 win in Austria.
It was overshadowed by news of Haller's diagnosis of a testicular tumour, however, ruling him out indefinitely, after the 28-year-old travelled back to Dortmund for medical tests over the weekend and missed the game.
Terzic admitted it was hard to focus on the task at hand upon his discovery of the news as the team prepared to depart for the match, but wished the Ivory Coast international a speedy recovery.
"The week went very well until yesterday," Terzic said on Tuesday. "The message from Sebastien Haller shocked us. Personally, I found out about half an hour before leaving for the game.
"Accordingly, it wasn't easy for us to think about tactics, pressing and passing again. We still tried to make it as professional as possible. We didn't talk to the team about it before the game, but informed the team afterwards.
"Sebastien Haller left us yesterday and traveled to Germany for further investigations. We keep our fingers crossed for Sebastien and the entire Haller family that he will recover as soon as possible."
Initially taking over from Lucien Favre in December 2020, Terzic was reappointed as the first team coach on a permanent basis in the off-season following Marco Rose's departure.
The 39-year-old revealed he has experienced a smoother transition into the role as Dortmund boss, despite Haller's recent diagnosis.
While he believes it will take time for his BVB side to be truly ready for the season ahead, the added time to work on patterns of play has made his job less chaotic.
"The biggest difference is that when I first became head coach, I was told on a Sunday morning and we had an away game on Tuesday night," Terzic said.
"You couldn't prepare many things and decided a lot quickly and intuitively. We now have weeks of advance notice to plan this preparation and the match opponents, to shape the group and to promote the integration of the newcomers. That's a key difference.
"The preparations won't be finished next Friday either, but it will still take some time before we're where we want to be at the end and we're showing consistently good football with a lot of automatisms. It will still take a little time, but we are on the right track."