The Reds let in three goals in the second half at Anfield as they were beaten for the first time in the competition this season.
"We are just disappointed that having controlled the game for long periods we gave away such poor goals," Rodgers told BBC Sport.
"I thought the team worked very well but we can't have to score three, four or five goals to win games. That is the area we have to work on. We concede goals too easily."
The loss has left the Merseysiders third in Group A after two games.