As it happened, Messi came off the bench to play a big part in Pedro's equaliser in the 1-1 draw that saw Barcelona through to the semi-finals on away goals.
"We scored and had a chance to make it two," Leonardo told AS.
"We had the Camp Nou trembling, and that is massive. I think Barcelona were frightened during the game.
"I'm sure that if Messi had been on our side we would have won 6-0."
Barcelona will play Bayern Munich in the semi-finals.