Deschamps guided the team to their first French league title since 1992 last season and he turned down a recent offer from Liverpool before extending his contract until June 2012.
"We, of course, want to qualify for the Champions League because it's essential sportingly and financially but the national competitions will be our priority because we can't compete with the big European clubs," the 41-year-old told Reuters in an interview.
"We can vie with them on one game but not over a long competition because there is a gulf between them and us. We'll still try to reach the second phase of the Champions League but it will depend on the draw."
The Ligue 1 season kicks off on Saturday and Marseille should have an easy opening game as they host promoted Caen but Deschamps is approaching the new campaign with utmost caution.
"In our sport, to win a title is difficult but to keep it is even more difficult," he said.
"The main thing is we can rely on a squad at least as strong as last season but we are now the title holders and we shall have to assume our rank weekend after weekend."
'NOT IN HEAVEN'
Deschamps, who captained Marseille to a Champions League triumph in 1993, was renowned for his total commitment to club and country as a player. His charges know they will not be allowed to behave like this year's France World Cup squad.
"I told them that we were not in heaven and that we had to start again from scratch with humility and the will to improve," said Deschamps.
"It will be a very long season, we'll be the team to beat and there will be five or six teams who will once again fight for the title and a European berth."
Deschamps was handed the freedom of the city of Marseille after coaching the team to the league title and the club offered him a long-term future in June.
He, however, opted for a shorter-term deal and also said he had refused an offer from Liverpool.
"A coach never knows when his job will end. I decided to stay with Marseille without asking for guarantees and I wasn't given precise objectives either," he said.
"They (Liverpool) approached me 48 hours before we resumed training. I was flattered and I had a good thought but my choice was obvious."
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