Darcheville came on as a second-half substitute for Sasa Papac as the Light Blues trailed to Sidney Govou's first-half goal.
After seeing Steven Whittaker clear a Karim Benzema shot off the line, Darcheville found himself only six yards from goal when skipper Barry Ferguson's cross from the right sped across the Lyon goal. With the Rangers fans ready to acclaim the equaliser that would have sent them into the last 16, Darcheville somehow blasted his effort over the bar.
He said: "I am a striker with a lot of experience and I know just how important that moment was in the game. I was sure I was going to score and I couldn't believe that I did not.
"I don't want to give any excuses but there was a little bounce of the ball just before I hit it. But I should have scored and if I had it would have given Rangers a great chance to qualify.
"This is the Champions League and I know at this level you do not get five or six chances in a game. When you get one like that you must take it. It is the most disappointing moment of my career and I am very, very unhappy.
"I knew the importance of this game to Rangers and the supporters. It was a massive game for the club and it would have meant so much to us if we had gone into the next stage of the Champions League."