The Glasgow giants face Swedish side Elfsborg in the first leg of their third round qualifying match on Wednesday, having already seen off the challenge of Cliftonville in the last round.
The Bhoys reached the last 16 of the competition last season, but Ledley still believes that they will need to be at their best to reach the group stage this time around.
"It's massive and can kick-start our season as well. It's one of the best competitions to be in and we know how difficult it is," he told reporters.
"Last season it was very difficult to qualify and it will be the same this year. We just need to give 100% and keep a clean sheet and you never know."
Ledley's future at Celtic has come under doubt recently following reports linking him with a £3m return to Cardiff City.