Saturday's 1-0 home defeat by Aston Villa should help the Premier League side avoid any complacency and the manner of it convinced Rodgers that his new-look defence must improve.
Liverpool have kept a clean sheet in only one of their four games this season and two in 13 going back to last March.
"We need to be better in those areas," the manager admitted.
"We were disappointed with how we conceded a goal at the weekend. We had five players making their Anfield debut and the cohesion does take a little bit of time."
It will be Rodgers's first match in charge for any Champions League tie and Liverpool's first since December 2009.
"Five years is a long time, probably too long," he said.
"When I came here my main priority was to get the club back to this level.
"We want to be at the elite level and the Champions League is that."
Asked about Ludogorets, Bulgarian champions for the past three seasons, who came through three qualifying rounds, he said: "They play an open, attacking style and they'll come here with confidence.
"They've worked hard to get here and we know they'll be excited about coming to Anfield, one of the most iconic stadiums in the world."
Rodgers confirmed that Slovakian centre half Martin Skrtel will not be ready to return, but there are no new injury concerns.
(Writing by Steve Tongue, editing by Ed Osmond)
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