Marquinhos warned Paris Saint-Germain's attitude must be spot-on at Borussia Dortmund after they stumbled to a 4-4 draw against Amiens on Saturday.
A shabby performance from the Ligue 1 leaders was not the way in which Thomas Tuchel's side wanted to prepare for Tuesday's Champions League last-16 match in Germany.
There seems no prospect of PSG losing their grip on top spot domestically; however, their burning ambition is to succeed in Europe.
And a repeat of the display at Amiens would almost certainly be punished ruthlessly by Dortmund, who have the likes of Erling Haaland and Jadon Sancho in their ranks.
Defender Marquinhos came off the bench at Amiens where PSG trailed 3-1 and turned the game around to lead 4-3, before shipping a late equaliser to a team who have not won in the league since November.
Brazil international Marquinhos, fit again after a hamstring injury, said: "We saw that if we aren't focused at the start of a game, we can concede goals and that could cost us dearly in the end.
"We need to keep in mind the team's good reaction, because it was important to get back on level terms. It shows you have to keep your concentration right to the end, because if you just drop off for just a second, you concede a goal at the end of the game."
Marquinhos told PSG's website: "It was important for me to play again, to get back into things ahead of the important game coming up. I'm very happy to have managed that before the big match ahead of us.
"We now have to turn to Dortmund, we have to think about playing well, and that we're all 100 per cent there, even if there have been some difficult situations before that game. We need to have a good attitude to put in a good performance."