The Frenchman had hoped to be leading Les Gones into the group stages of the Champions League, but all of last season's hard work was undone when they were knocked out in the qualifiers by Real Sociedad.
However, Garde admitted that his side were well and truly second best and is now looking to mount a serious challenge in the Europa League.
"I think we have to admit that having lost 2-0 twice the opponent was stronger than us," the 47-year-old told L'Equipe.
"I would have preferred the squad to grow in the Champions League although it would have been difficult for us. It will now develop in the Europa League, a competition which is a little bit more achievable.
"During this transitional period, we know there will be times when we suffer and this is a difficult period but it is not every day when we face an opponent of the calibre of Real Sociedad."
The draw for the group stages of the Europa League takes place in Monaco later today.