A 1-1 draw at Valenciennes at the weekend did little to lift the pressure which has been mounting on the former Monaco and Juventus coach after a start to the season which has brought just one win in eight Ligue 1 matches.
Conceding a late equaliser on Saturday will have been particularly hard to stomach, but Deschamps still has faith in his side.
"Our spirits are generally high," he told the La Depeche newspaper.
"We put a lot of heart and enthusiasm into the match and they were two points lost in view of the situation.
"I am sorry for my players because we punished ourselves at the worst possible time.
"We were in control of 99% of the match, but now we have to lift ourselves up for the match in the Champions League."
Marseille currently top Group F thanks to a 1-0 win at Olympiacos a fortnight ago, but their hopes of making it two wins from two have suffered a setback with the news that both Andre-Pierre Gignac and Benoit Cheyrou will miss the game due to injury.
Conversely, Dortmund coach Jurgen Klopp could welcome his side's top goalscorer from last season, Lucas Barrios, into his squad on Wednesday night.
The Paraguay international has yet to play this season after picking up an injury at the Copa America in the summer, but he has now returned to training and is a candidate for a place on the bench at the Stade Velodrome.
"If we can avoid it, Lucas will not be in the starting XI," said Klopp, who is only being cautious about the fitness of his star striker and not so much about Wednesday's opponents.
"They have remained much further behind the expectations than we have."
Dortmund picked up a morale-boosting 2-1 win over Mainz at the weekend, although Klopp is reading little into that result.
"We are keeping the Champions League completely separate from the Bundesliga so we should not make it out as if that win gives us a huge advantage," he said.
Ivan Perisic, who scored Dortmund's equaliser in a 1-1 draw with Arsenal a fortnight ago and opened his account in the Bundesliga at the weekend, should keep his starting berth in the heart of the Dortmund midfield.
That means Germany international Kevin Grosskreutz will have to settle for a place on the bench, alongside Barrios.