Thomas Tuchel said the ongoing absence of fans is proving difficult as the Paris Saint-Germain head coach highlighted the struggles of playing behind closed doors following Tuesday's Champions League defeat.
PSG – last season's Champions League runners-up – lost 2-1 to Premier League visitors Manchester United in their Group H opener at Parc des Princes.
Marcus Rashford's 87th-minute strike downed PSG, who equalised 10 minutes into the second half via Anthony Martial's own goal after United captain Bruno Fernandes had converted a 23rd-minute penalty.
The result condemned PSG to their first home loss in the Champions League group stage in 25 games, and PSG boss Tuchel bemoaned behind-closed-doors football amid the coronavirus pandemic.
"It's clear we can improve and we must," Tuchel told reporters. "It's clear that we're not happy with the performance but now is not the moment to be too critical, here, in public.
"We'll do that behind closed doors. We have a lot of things to improve. I don't know why but it's obvious that we had trouble to find the required spirit.
"It's really difficult to always play in closed doors, it's very difficult, it's not the same atmosphere in Champions League. It's one reason but it's not the decisive reason. We'll analyse and discuss but behind closed doors."
PSG – without the likes of Marquinhos and Marco Verratti – were far from their best in the French capital, where star duo Neymar and Kylian Mbappe were nullified by United's defence.
Neymar failed to score in four consecutive Champions League appearances for the first time since November 2013.
PSG – who will also meet last season's semi-finalists RB Leipzig – have the chance to respond when they travel to Group H opponents Istanbul Basaksehir next week.
"I didn't need the proof, I knew it was a difficult group," Tuchel said. "I knew that, I knew that very well. I know what we missed. We had injured players, players who already proved what they are able to do. We tried, but I'll always defend my players, because they are the same players who have done well in the last weeks, the last months.
"Today, it was like that… We had trouble finding solutions and the spirit that's necessary in the Champions League. Now, it’s more difficult than before [in the group]."
PSG defender Presnel Kimpembe, who captained the Ligue 1 champions, told RMC Sport: "There is no explanation. We were simply not good tonight, we were not in the duels and we were slow and late in running back defensively, you pay for that at this level. We can only look at ourselves."