The Ligue 1 side suffered a 2-0 home defeat against their Spanish counterparts in their play-off first-leg encounter, with their misery further compounded when Milan Bisevac was sent off was sent off 15 minutes from time for a second bookable offence.
Frenchman Antoine Griezmann put the visitors in front in the 17th minute with an acrobatic effort and the advantage was doubled in the 50th minute when Haris Seferovic's volley caught out goalkeeper Anthony Lopes to leave Lyon facing an uphill mountain in the return leg.
Garde said to the club's official website: "I'm disappointed but I think we played a great team and were not expecting such an opposition. We thought we would be above them physically but it was just the opposite.
"It was a bad start to the game. They scored spectacular goals. Their victory is deserved. I wished that we could have reduced the score to move into better conditions.
"The quality of play and excitement of previous matches can give me a little hope. We still have 90 minutes. There is hope and we'll be there to exploit it."
Chairman Jean-Michel Aulas echoed his manager's thoughts.
"We came across a very good team, more sharp than previously thought," he said.
"It is half-time of a game that went wrong here.We need to return to work on Saturday against Stade de Reims."